Treat `pytest` warnings as errors #455

Job	Run time
Test with nox (ubuntu-20.04, 3.11, ci_checks_max)	6m 11s
Build distribution packages	15s
Test documentation website generation	0s
Test with nox (ubuntu-20.04, 3.11, pytest_min)	5m 54s
Cross-arch tests with nox (arm64, ubuntu-20.04, 3.11, pytest_min)	4m 18s
Cross-arch tests with nox (arm64, ubuntu-20.04, 3.11, pytest_max)	4m 20s
Test package installation in different architectures	1m 29s
Cross-arch tests with nox	1s
Test with nox	1s
Publish documentation website to GitHub pages	0s
Create GitHub release	0s
Publish packages to PyPI	0s
	22m 29s

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