GitHub Actions: setup-python allow-prereleases for Py3.12 #325

Job	Run time
integration (macos-latest, 3.8)	2m 25s
integration (macos-latest, 3.x)	2m 4s
integration (macos-latest, 3.12)	3m 0s
integration (ubuntu-latest, 3.8)	1m 32s
integration (ubuntu-latest, 3.x)	1m 18s
integration (ubuntu-latest, 3.12)	1m 56s
integration (windows-latest, 3.8)	20m 52s
integration (windows-latest, 3.x)	17m 47s
integration (windows-latest, 3.12)	28m 0s
	1h 18m 54s

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