Description of problem:
`firefox` is needed for tests during %check. Which is not available on armv7hl.

Version-Release number of selected component (if applicable):
3.142.7

How reproducible:
100%

Steps to Reproduce:
1. run koji build for rubygem-selenium-webdriver.


Actual results:
```
DEBUG package_manager.py:194:  ['/usr/bin/dnf', 'builddep', '--installroot', '/var/lib/mock/f33-build-20890394-1545760/root/', '--setopt=install_weak_deps=0', '--disableplugin=local', '--disableplugin=spacewalk', '/var/lib/mock/f33-build-20890394-1545760/root//builddir/build/SRPMS/rubygem-selenium-webdriver-3.142.7-1.fc33.src.rpm']
DEBUG util.py:772:  child environment: None
DEBUG util.py:698:  Executing command: ['/usr/bin/dnf', 'builddep', '--installroot', '/var/lib/mock/f33-build-20890394-1545760/root/', '--setopt=install_weak_deps=0', '--disableplugin=local', '--disableplugin=spacewalk', '/var/lib/mock/f33-build-20890394-1545760/root//builddir/build/SRPMS/rubygem-selenium-webdriver-3.142.7-1.fc33.src.rpm', '--setopt=tsflags=nocontexts'] with env {'TERM': 'vt100', 'SHELL': '/bin/bash', 'HOME': '/var/lib/mock/f33-build-20890394-1545760/rpmconfig', 'HOSTNAME': 'mock', 'PATH': '/usr/bin:/bin:/usr/sbin:/sbin', 'PROMPT_COMMAND': 'printf "\\033]0;<mock-chroot>\\007"', 'PS1': '<mock-chroot> \\s-\\v\\$ ', 'LANG': 'C.UTF-8', 'LC_MESSAGES': 'C.UTF-8', 'LD_PRELOAD': '/var/tmp/tmp.mock.w2llrt6p/$LIB/nosync.so'} and shell False
DEBUG util.py:600:  No matches found for the following disable plugin patterns: local, spacewalk
DEBUG util.py:602:  Last metadata expiration check: 0:00:01 ago on Mon May 25 16:22:04 2020.
DEBUG util.py:600:  No matching package to install: 'firefox'
DEBUG util.py:600:  Not all dependencies satisfied
DEBUG util.py:600:  Error: Some packages could not be found.
DEBUG util.py:753:  Child return code was: 1
```

Expected results:
firefox installed.

Additional info:
https://koji.fedoraproject.org/koji/taskinfo?taskID=44959157