Bump coverage from 6.3 to 6.3.1 in /requirements

Bumps [coverage](https://github.com/nedbat/coveragepy) from 6.3 to 6.3.1.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](nedbat/coveragepy@6.3...6.3.1)

---
updated-dependencies:
- dependency-name: coverage
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

requirements/coverage.txt

@@ -1,2 +1,2 @@
-coverage==6.3
+coverage==6.3.1
 toml==0.10.2