Add Python 3.15 test infrastructure #2458

Job	Run time
stub_uploader tests	4m 53s
stubtest: third party (ubuntu-latest, 2)	11m 12s
stubtest: third party (ubuntu-latest, 0)	5m 54s
stubtest: third party (ubuntu-latest, 3)	9m 56s
stubtest: third party (ubuntu-latest, 1)	6m 14s
stubtest: third party (windows-latest, 1)	1m 34s
stubtest: third party (macos-latest, 1)	1m 34s
stubtest: third party (macos-latest, 0)	1m 4s
stubtest: third party (windows-latest, 0)	1m 34s
stubtest: stdlib (ubuntu-latest, 3.14)	38s
stubtest: third party (windows-latest, 2)	2m 13s
stubtest: stdlib (ubuntu-latest, 3.12)	33s
stubtest: stdlib (ubuntu-latest, 3.15)	45s
stubtest: stdlib (macos-latest, 3.10)	42s
stubtest: third party (windows-latest, 3)	1m 39s
stubtest: stdlib (ubuntu-latest, 3.11)	35s
stubtest: stdlib (windows-latest, 3.14)	1m 7s
stubtest: stdlib (windows-latest, 3.13)	1m 23s
stubtest: third party (macos-latest, 2)	53s
stubtest: stdlib (ubuntu-latest, 3.13)	38s
stubtest: stdlib (macos-latest, 3.15)	53s
stubtest: stdlib (windows-latest, 3.12)	1m 10s
stubtest: stdlib (macos-latest, 3.13)	26s
stubtest: stdlib (windows-latest, 3.11)	1m 13s
stubtest: stdlib (ubuntu-latest, 3.10)	36s
stubtest: stdlib (macos-latest, 3.12)	50s
stubtest: stdlib (windows-latest, 3.15)	2m 1s
stubtest: third party (macos-latest, 3)	1m 15s
stubtest: stdlib (macos-latest, 3.11)	39s
stubtest: stdlib (macos-latest, 3.14)	23s
Create issue on failure	0s
	1h 4m 27s

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