Add Python 3.15 test infrastructure #2459

Job	Run time
stub_uploader tests	5m 4s
stubtest: third party (ubuntu-latest, 1)	6m 18s
stubtest: third party (windows-latest, 3)	1m 24s
stubtest: third party (macos-latest, 3)	1m 25s
stubtest: third party (macos-latest, 0)	1m 14s
stubtest: third party (ubuntu-latest, 2)	7m 9s
stubtest: third party (macos-latest, 1)	48s
stubtest: third party (windows-latest, 1)	1m 38s
stubtest: third party (macos-latest, 2)	54s
stubtest: third party (ubuntu-latest, 0)	5m 39s
stubtest: third party (ubuntu-latest, 3)	9m 22s
stubtest: stdlib (macos-latest, 3.10)	1m 6s
stubtest: stdlib (ubuntu-latest, 3.11)	36s
stubtest: stdlib (ubuntu-latest, 3.10)	37s
stubtest: stdlib (ubuntu-latest, 3.14)	40s
stubtest: third party (windows-latest, 2)	2m 6s
stubtest: stdlib (windows-latest, 3.13)	1m 18s
stubtest: stdlib (ubuntu-latest, 3.15)	49s
stubtest: stdlib (macos-latest, 3.12)	26s
stubtest: stdlib (ubuntu-latest, 3.13)	43s
stubtest: stdlib (windows-latest, 3.15)	1m 55s
stubtest: stdlib (macos-latest, 3.15)	55s
stubtest: stdlib (windows-latest, 3.11)	2m 23s
stubtest: stdlib (macos-latest, 3.14)	32s
stubtest: stdlib (windows-latest, 3.12)	1m 41s
stubtest: stdlib (windows-latest, 3.14)	1m 3s
stubtest: stdlib (macos-latest, 3.13)	38s
stubtest: stdlib (ubuntu-latest, 3.12)	42s
stubtest: stdlib (macos-latest, 3.11)	37s
stubtest: third party (windows-latest, 0)	1m 45s
Create issue on failure	0s
	1h 1m 27s

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