docs/changes: update for v0.5.5. #3714

Job	Run time
smoke (amaranth-lang/amaranth-boards)	36s
smoke (amaranth-lang/amaranth-soc)	46s
document	1m 2s
smoke (amaranth-lang/amaranth-stdio)	42s
check-links	53s
test (3.8)	3m 33s
test (3.9)	2m 49s
test (3.11)	3m 48s
test (3.10)	2m 38s
test (pypy-3.10)	6m 17s
test (3.12)	3m 47s
test (pypy-3.8)	5m 57s
test (pypy-3.9)	5m 32s
test (3.13-dev)	4m 6s
publish-docs	22s
publish-docs-dev	-1s
required	2s
publish-package	31s
publish-schemas	5s
publish-release	3s
	43m 28s

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