Tests

Bump actions/setup-python from 5 to 6 #1615

Job	Run time
docker	2s
(ubuntu-latest, Py3.8, sk0.23.1, sk-only:false)	2s
(windows-latest, Py, sk0.24.*, sk-only:false)	3s
(ubuntu-latest, Py3.11, sk1.3.*, sk-only:true)	1m 59s
(ubuntu-latest, Py3.11, sk1.5.*, sk-only:true)	1m 51s
(ubuntu-latest, Py3.11, sk1.4.*, sk-only:true)	1m 43s
	5m 40s

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