docs/changes: update for v0.5.5. #3709

Job	Run time
document	1m 0s
smoke (amaranth-lang/amaranth-stdio)	1m 0s
smoke (amaranth-lang/amaranth-soc)	1m 0s
test (3.9)	2m 34s
smoke (amaranth-lang/amaranth-boards)	42s
test (3.10)	3m 14s
test (3.12)	3m 43s
test (3.13)	3m 35s
test (pypy-3.10)	4m 30s
test (pypy-3.9)	5m 45s
test (3.11)	3m 48s
check-links	49s
test (3.14-dev)	31s
publish-docs	6s
publish-docs-dev	-1s
required	3s
publish-schemas	8s
publish-package	11s
publish-release	0s
	32m 38s

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