Update coverage requirement from ==7.6.* to ==7.8.*

Updates the requirements on [coverage](https://github.com/nedbat/coveragepy) to permit the latest version.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](nedbat/coveragepy@7.6.0...7.8.0)

---
updated-dependencies:
- dependency-name: coverage
  dependency-version: 7.8.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements-test.txt

@@ -1,3 +1,3 @@
-coverage == 7.6.*
+coverage == 7.8.*
 pre-commit == 4.0.*
 tox == 4.22.*