[deps] Update pytest-cov requirement from ~=5.0.0 to ~=6.0.0

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-test.txt

@@ -1,6 +1,6 @@
 pytest-django~=4.9.0
 pytest-asyncio~=0.24.0
-pytest-cov~=5.0.0
+pytest-cov~=6.0.0
 openwisp-utils[qa,selenium]~=1.1.1
 channels_redis~=4.2.1
 django_redis~=5.4.0