Update pytest-cov requirement from <5.0.0,>=2.6.1 to >=2.6.1,<7.0.0

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@v2.6.1...v6.0.0)

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

Signed-off-by: dependabot[bot] <support@github.com>

requirements/dev.txt

@@ -6,7 +6,7 @@ types-requests>=2.25, <3.0
 types-toml>=0.10, <1.0
 # testing
 pytest>=5.3.5, <8.0.0
-pytest-cov>=2.6.1, <5.0.0
+pytest-cov>=2.6.1, <7.0.0
 pytest-xdist>=1.28.0, <4.0.0 # for distributed testing, currently unused (see setup.cfg)
 pytest_cases>=3.6.8, <4.0.0
 pytest-randomly>=3.5.0, <4.0.0