Bump coverage from 5.3.1 to 5.4

Bumps [coverage](https://github.com/nedbat/coveragepy) from 5.3.1 to 5.4.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](https://github.com/nedbat/coveragepy/compare/coverage-5.3.1...coverage-5.4)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

requirements-dev.txt

@@ -4,7 +4,7 @@ async-timeout==3.0.1
 pytest==6.2.1
 pytest-cov==2.10.1
 pytest-mock==3.4.0
-coverage==5.3.1
+coverage==5.4
 sphinx==3.4.1
 pep257==0.7.0
 aiohttp-session==2.9.0