EXPERIMENTAL: Add tutorial testing workflows integrated with Sphinx docs #3650

Job	Run time
smoke (amaranth-lang/amaranth-boards)	31s
smoke (amaranth-lang/amaranth-stdio)	50s
document	46s
smoke (amaranth-lang/amaranth-soc)	57s
test (3.10)	2m 24s
check-links	54s
test (3.12)	3m 23s
test (3.13)	3m 18s
test (3.14-dev)	1m 57s
test (pypy-3.9)	4m 42s
test (3.9)	2m 23s
test (pypy-3.10)	4m 49s
test (3.11)	2m 49s
publish-docs-dev	0s
publish-docs	0s
required	3s
publish-schemas	0s
publish-package	0s
publish-release	0s
	29m 46s

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