Update coverage requirement in the all-dependencies group

Updates the requirements on [coverage](https://github.com/nedbat/coveragepy) to permit the latest version.

Updates `coverage` to 7.6.0
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](nedbat/coveragepy@7.5.0...7.6.0)

---
updated-dependencies:
- dependency-name: coverage
  dependency-type: direct:production
  dependency-group: all-dependencies
...

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

requirements-test.txt

@@ -1,7 +1,7 @@
 # This file prepares the pytest and coverage env and is used by tox.ini
 codecov~=2.1
 cov-core~=1.15
-coverage~=7.5
+coverage~=7.6
 flake8~=7.1
 mock~=5.1
 pytest~=8.2