CI: require tests to pass on Python 3.14. #3793

Job	Run time
document	59s
smoke (amaranth-lang/amaranth-stdio)	54s
smoke (amaranth-lang/amaranth-soc)	55s
check-links	1m 1s
test (3.9)	4m 0s
test (3.11)	3m 27s
test (3.10)	3m 16s
test (3.12)	5m 46s
test (3.13)	4m 26s
test (pypy-3.9)	6m 21s
test (3.14)	3m 36s
test (pypy-3.10)	6m 57s
smoke (amaranth-lang/amaranth-boards)	46s
test (3.15-dev)	5s
test (pypy-3.11)	6m 9s
publish-docs	21s
publish-docs-dev	-1s
required	4s
publish-package	34s
publish-schemas	14s
publish-release	-1s
	49m 49s

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