Update pytest-cov requirement from ^3.0.0 to ^4.0.0

Updates the requirements on [pytest-cov](https://github.com/pytest-dev/pytest-cov) to permit the latest version.
- [Release notes](https://github.com/pytest-dev/pytest-cov/releases)
- [Changelog](https://github.com/pytest-dev/pytest-cov/blob/master/CHANGELOG.rst)
- [Commits](pytest-dev/pytest-cov@v3.0.0...v4.0.0)

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

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

Author: dependabot[bot]

pyproject.toml

@@ -53,7 +53,7 @@ mypy = "^0.971"
 isort = "^5.6.4"
 doc8 = "^0.11.0"
 darglint = "^1.5.7"
-pytest-cov = "^3.0.0"
+pytest-cov = "^4.0.0"
 pylint = "^2.6.0"
 sphinx-argparse = "^0.3.0"
 deepdiff = "^5.2.3"