Move six to deps to prevent a potential future disaster, uv.lock #1143

Job	Run time
run-test-suite (ubuntu-latest, 3.9, 9.4)	11m 16s
run-test-suite (ubuntu-latest, 3.9, latest)	11m 39s
run-test-suite (ubuntu-latest, 3.13, latest)	12m 4s
run-test-suite (ubuntu-22.04, 3.7, 9.1)	9m 40s
	44m 39s

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