Add Python 3.15 test infrastructure #2455

Job	Run time
stub_uploader tests	3m 34s
stubtest: third party (macos-latest, 0)	50s
stubtest: third party (macos-latest, 3)	58s
stubtest: third party (windows-latest, 1)	1m 31s
stubtest: third party (ubuntu-latest, 0)	3m 32s
stubtest: third party (macos-latest, 1)	47s
stubtest: third party (ubuntu-latest, 1)	3m 38s
stubtest: third party (windows-latest, 2)	2m 36s
stubtest: third party (ubuntu-latest, 3)	3m 27s
stubtest: stdlib (ubuntu-latest, 3.11)	41s
stubtest: third party (ubuntu-latest, 2)	3m 37s
stubtest: stdlib (ubuntu-latest, 3.10)	40s
stubtest: third party (macos-latest, 2)	47s
stubtest: third party (windows-latest, 0)	1m 36s
stubtest: stdlib (windows-latest, 3.13)	1m 5s
stubtest: stdlib (windows-latest, 3.14)	1m 45s
stubtest: stdlib (ubuntu-latest, 3.13)	36s
stubtest: stdlib (ubuntu-latest, 3.15)	1m 29s
stubtest: stdlib (macos-latest, 3.13)	26s
stubtest: third party (windows-latest, 3)	1m 52s
stubtest: stdlib (windows-latest, 3.15)	1m 40s
stubtest: stdlib (macos-latest, 3.15)	48s
stubtest: stdlib (ubuntu-latest, 3.12)	36s
stubtest: stdlib (macos-latest, 3.12)	35s
stubtest: stdlib (macos-latest, 3.14)	27s
stubtest: stdlib (macos-latest, 3.10)	49s
stubtest: stdlib (ubuntu-latest, 3.14)	34s
stubtest: stdlib (macos-latest, 3.11)	36s
stubtest: stdlib (windows-latest, 3.11)	1m 29s
stubtest: stdlib (windows-latest, 3.12)	1m 9s
Create issue on failure	1s
	44m 11s

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