Update coverage requirement from ~=7.8 to ~=7.9 (#10430)

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](coveragepy/coveragepy@7.8.0...7.9.1)

---
updated-dependencies:
- dependency-name: coverage
  dependency-version: 7.9.1
  dependency-type: direct:production
...

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Author: dependabot[bot]

requirements_test.txt

@@ -1,5 +1,5 @@
 -r requirements_test_min.txt
-coverage~=7.8
+coverage~=7.9
 tbump~=6.11.0
 contributors-txt>=1.0.0
 pytest-cov~=6.2