docs/changes: Add RFC 66 changes. #3557

Job	Run time
check-links	47s
document	47s
smoke (amaranth-lang/amaranth-boards)	38s
test (3.8)	2m 20s
smoke (amaranth-lang/amaranth-stdio)	46s
test (3.9)	2m 17s
smoke (amaranth-lang/amaranth-soc)	40s
test (3.10)	2m 16s
test (3.11)	2m 41s
test (3.12)	3m 23s
test (pypy-3.8)	5m 16s
test (pypy-3.9)	4m 56s
test (pypy-3.10)	5m 6s
test (3.13-dev)	3m 4s
publish-docs	4s
publish-docs-dev	0s
required	1s
publish-schemas	9s
publish-package	40s
publish-release	0s
	35m 51s

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