Bump coverage from 6.3 to 6.3.1

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](coveragepy/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] <support@github.com>

Author: dependabot[bot]

requirements-test.txt

@@ -1,7 +1,7 @@
 # test runs requirements (versions we'll be testing against) - automatically updated by requires.io
 pip>=9  # minimum installation requirements
 setuptools>=21  # minimum installation requirements
-coverage==6.3 # pytest-cov
+coverage==6.3.1 # pytest-cov
 pytest==6.2.5
 pytest-cov==3.0.0
 pytest-xdist==2.5.0