chore(deps): update pytest-cov requirement from ==5.* to ==6.*

Updates the requirements on [pytest-cov](https://github.com/pytest-dev/pytest-cov) to permit the latest version.
- [Changelog](https://github.com/pytest-dev/pytest-cov/blob/master/CHANGELOG.rst)
- [Commits](pytest-dev/pytest-cov@v5.0.0...v6.0.0)

---
updated-dependencies:
- dependency-name: pytest-cov
  dependency-type: direct:production
...

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

requirements-testing.txt

@@ -2,7 +2,7 @@ black == 24.*
 coverage[toml] == 7.*
 mypy == 1.*
 pytest == 8.*
-pytest-cov == 5.*
+pytest-cov == 6.*
 pytest-xdist == 3.*
 ruff == 0.4.*
 twine == 5.*