Fixed and worked around some dependency issues to get FastAPI working on Python 3.12. Now:

$ fedpkg mockbuild --enablerepo=local

Error: 
 Problem 1: package python3-celery-5.3.1-1.fc39.noarch from fedora requires python(abi) = 3.11, but none of the providers can be installed
  - package python3-devel-3.12.0~b3-2.fc39.x86_64 from local conflicts with python3 < 3.12.0~b3-2.fc39 provided by python3-3.11.4-1.fc39.i686 from fedora
  - package python3-devel-3.12.0~b3-2.fc39.x86_64 from local conflicts with python3 < 3.12.0~b3-2.fc39 provided by python3-3.11.4-1.fc39.x86_64 from fedora
  - cannot install the best candidate for the job
 Problem 2: package python3-flask-login-0.6.2-2.fc39.noarch from fedora requires python3.11dist(flask) >= 1.0.4, but none of the providers can be installed
  - cannot install both python3-flask-1:2.2.5-2.fc39.noarch from local and python3-flask-1:2.2.5-1.fc39.noarch from fedora
  - cannot install the best candidate for the job
 Problem 3: package python3-opentelemetry-api-1.18.0-2.fc39.noarch from fedora requires python3.11dist(setuptools) >= 16, but none of the providers can be installed
  - cannot install both python3-setuptools-67.7.2-5.fc39.noarch from local and python3-setuptools-67.7.2-2.fc39.noarch from fedora
  - package python3-opentelemetry-distro-1:0.39~b0-16.fc39.noarch from fedora requires (python3.11dist(opentelemetry-api) >= 1.12 with python3.11dist(opentelemetry-api) < 2), but none of the providers can be installed
  - package python3-gevent-22.10.2-3.fc39.x86_64 from local requires python3.12dist(setuptools), but none of the providers can be installed
  - cannot install the best candidate for the job

$ fedpkg mockbuild --enablerepo=local

=================================== FAILURES ===================================
_______________________ test_breadcrumb_extra_scrubbing ________________________
tests/test_scrubber.py:103: in test_breadcrumb_extra_scrubbing
    assert event["breadcrumbs"]["values"][0]["data"] == {
E   AssertionError: assert {'foo': 42, '...skName': None} == {'foo': 42, '... '[Filtered]'}
E     Omitting 2 identical items, use -vv to show
E     Left contains 1 more item:
E     {'taskName': None}
E     Use -v to get more diff
------------------------------ Captured log call -------------------------------
INFO     tests.test_scrubber:test_scrubber.py:95 bread
CRITICAL tests.test_scrubber:test_scrubber.py:96 whoops
___________________________ test_logging_extra_data ____________________________
tests/integrations/logging/test_logging.py:64: in test_logging_extra_data
    assert event["extra"] == {"bar": 69}
E   AssertionError: assert {'bar': 69, 'taskName': None} == {'bar': 69}
E     Omitting 1 identical items, use -vv to show
E     Left contains 1 more item:
E     {'taskName': None}
E     Use -v to get more diff
------------------------------ Captured log call -------------------------------
INFO     test_logging:test_logging.py:58 bread
CRITICAL test_logging:test_logging.py:59 lol
_____________________ test_logging_extra_data_integer_keys _____________________
tests/integrations/logging/test_logging.py:79: in test_logging_extra_data_integer_keys
    assert event["extra"] == {"1": 1}
E   AssertionError: assert {'1': 1, 'taskName': None} == {'1': 1}
E     Omitting 1 identical items, use -vv to show
E     Left contains 1 more item:  
E     {'taskName': None}
E     Use -v to get more diff
------------------------------ Captured log call -------------------------------
CRITICAL test_logging:test_logging.py:75 integer in extra keys
________________________ test_logging_captured_warnings ________________________
tests/integrations/logging/test_logging.py:194: in test_logging_captured_warnings
    assert len(events) == 2
E   AssertionError: assert 4 == 2 
E    +  where 4 = len([{'breadcrumbs': {'values': []}, 'contexts': {'trace': {'parent_span_id': None, 'span_id': '951db6cb792b6ac2', 'trace_...fc89639000b4441c9fc3c1de90f74734'}}, 'environment': 'production', 'event_id': '4634c0a5fe874924b478908aaef93e31', ...}])
------------------------------ Captured log call -------------------------------
WARNING  py.warnings:warnings.py:109 /builddir/build/BUILD/sentry-python-1.27.0/tests/integrations/logging/test_logging.py:188: UserWarning: first
  warnings.warn("first")

WARNING  py.warnings:warnings.py:109 /builddir/build/BUILD/sentry-python-1.27.0/sentry_sdk/client.py:261: DeprecationWarning: datetime.utcnow() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.now(datetime.UTC).
  event["timestamp"] = datetime.utcnow()

WARNING  py.warnings:warnings.py:109 /builddir/build/BUILD/sentry-python-1.27.0/sentry_sdk/integrations/logging.py:282: DeprecationWarning: datetime.utcfromtimestamp() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.fromtimestamp(timestamp, datetime.UTC).
  "timestamp": datetime.datetime.utcfromtimestamp(record.created),

WARNING  py.warnings:warnings.py:109 /builddir/build/BUILD/sentry-python-1.27.0/tests/integrations/logging/test_logging.py:189: UserWarning: second
  warnings.warn("second")
=============================== warnings summary ===============================

(massive spew of warnings)

============================= slowest 5 durations ==============================
2.75s call     tests/test_client.py::test_atexit[20]
2.35s call     tests/integrations/celery/test_celery.py::test_no_stackoverflows
1.76s call     tests/test_client.py::test_atexit[10]
0.77s call     tests/integrations/stdlib/test_subprocess.py::test_subprocess_basic[False-None-as_list-False]
0.77s call     tests/integrations/stdlib/test_subprocess.py::test_subprocess_basic[True-env_mapping1-as_list-False]
=========================== short test summary info ============================
FAILED tests/test_scrubber.py::test_breadcrumb_extra_scrubbing - AssertionErr...
FAILED tests/integrations/logging/test_logging.py::test_logging_extra_data - ...
FAILED tests/integrations/logging/test_logging.py::test_logging_extra_data_integer_keys
FAILED tests/integrations/logging/test_logging.py::test_logging_captured_warnings
== 4 failed, 942 passed, 18 skipped, 43 deselected, 27496 warnings in 39.58s ===

Confirmed FastAPI 0.100.0 (https://src.fedoraproject.org/rpms/python-fastapi/pull-request/7) will not introduce additional regressions.

The reason for first three tests breakage is: https://github.com/python/cpython/blob/4b4a5b70aa8d47b1e2a0582b741c31b786da762a/Misc/NEWS.d/3.12.0a1.rst?plain=1#L3660-L3661

I'm working on this.

FEDORA-2023-b7413dd384 has been submitted as an update to Fedora 39. https://bodhi.fedoraproject.org/updates/FEDORA-2023-b7413dd384

FEDORA-2023-b7413dd384 has been pushed to the Fedora 39 stable repository.
If problem still persists, please make note of it in this bug report.