Update pytest-cov requirement from ==2.12.* to >=2.12,<5.1

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@v2.12.0...v5.0.0)

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

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

setup.py

@@ -26,7 +26,7 @@
           'test': [
             'pylint==2.8.*',
             'pytest==6.2.*',
-            'pytest-cov==2.12.*',
+            'pytest-cov>=2.12,<5.1',
             'unify==0.5'
           ]
       },