build(deps-dev): update pytest-cov requirement (#924)

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...v4.1.0)

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

pyproject.toml

@@ -33,7 +33,7 @@ dev = [
     "pre-commit",
     "pytest",
     "pytest-snapshot",
-    "pytest-cov ~= 4.0.0",
+    "pytest-cov >= 4.0,< 4.2",
     "sphinx",
     "sphinx-rtd-theme",
 ]