Add Python 3.15 test infrastructure #2452

Job	Run time
stub_uploader tests	2m 29s
stubtest: third party (ubuntu-latest, 3)	2m 22s
stubtest: third party (macos-latest, 0)	1m 23s
stubtest: third party (ubuntu-latest, 1)	2m 22s
stubtest: third party (windows-latest, 1)	1m 42s
stubtest: third party (windows-latest, 2)	2m 6s
stubtest: third party (macos-latest, 1)	53s
stubtest: third party (macos-latest, 2)	50s
stubtest: third party (ubuntu-latest, 2)	2m 27s
stubtest: stdlib (ubuntu-latest, 3.11)	41s
stubtest: third party (windows-latest, 0)	1m 48s
stubtest: third party (ubuntu-latest, 0)	2m 20s
stubtest: third party (windows-latest, 3)	1m 42s
stubtest: third party (macos-latest, 3)	1m 20s
stubtest: stdlib (ubuntu-latest, 3.12)	35s
stubtest: stdlib (windows-latest, 3.15)	2m 22s
stubtest: stdlib (windows-latest, 3.12)	1m 42s
stubtest: stdlib (ubuntu-latest, 3.10)	59s
stubtest: stdlib (windows-latest, 3.13)	1m 10s
stubtest: stdlib (macos-latest, 3.14)	33s
stubtest: stdlib (macos-latest, 3.10)	44s
stubtest: stdlib (macos-latest, 3.12)	34s
stubtest: stdlib (macos-latest, 3.11)	22s
stubtest: stdlib (ubuntu-latest, 3.14)	37s
stubtest: stdlib (macos-latest, 3.15)	1m 8s
stubtest: stdlib (macos-latest, 3.13)	26s
stubtest: stdlib (windows-latest, 3.14)	1m 6s
stubtest: stdlib (windows-latest, 3.11)	1m 12s
stubtest: stdlib (ubuntu-latest, 3.13)	34s
stubtest: stdlib (ubuntu-latest, 3.15)	1m 27s
Create issue on failure	1s
	39m 57s

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