chore: 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] <[email protected]>

pyproject.toml

@@ -15,7 +15,7 @@ eagerx = "^0.1.33"
 [tool.poetry.dev-dependencies]
 black = "^22.1.0"
 pytest = "^7.0"
-pytest-cov = "^3.0.0"
+pytest-cov = "^4.0.0"
 flake8 = ">=3"
 flake8-bugbear = "^22.3.23"
 genbadge = "^1.1.0"