build(deps): update pytest-cov requirement from <5.1,>=4 to >=4,<6.1

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@v4.0.0...v6.0.0)

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

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

Author: dependabot[bot]

requirements/testing.txt

@@ -3,5 +3,5 @@
 
 GitPython>=3.1,<3.2
 Pillow>=10.4.0,<11.1
-pytest-cov>=4,<5.1
+pytest-cov>=4,<6.1
 validators>=0.29.0,<0.35