Bump coverage from 7.6.1 to 7.6.8 in /requirements (#1422)

Bumps [coverage](https://github.com/nedbat/coveragepy) from 7.6.1 to 7.6.8.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](nedbat/coveragepy@7.6.1...7.6.8)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements/coverage.txt

@@ -1,2 +1,2 @@
-coverage==7.6.1
+coverage==7.6.8
 toml==0.10.2