Unit tests

`CI PR #6:` GitHub CI/`tox`: Update CI to use Python `3.11`, `3.12` and `3.13` #661

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Run time

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Job	Run time
test (3.11, ubuntu-22.04)	52s
test (3.12, ubuntu-22.04)	58s
test (3.13, ubuntu-22.04)	1m 29s
finish-coverage-upload	5s
	3m 24s