Update changelog for v0.5.5 [v0.5.x backport] #3712

Job	Run time
document	58s
smoke (amaranth-lang/amaranth-boards)	35s
smoke (amaranth-lang/amaranth-stdio)	45s
test (3.8)	3m 8s
test (pypy-3.9)	6m 2s
test (3.9)	2m 29s
test (3.11)	2m 52s
test (3.10)	1m 57s
test (pypy-3.8)	5m 53s
test (pypy-3.10)	6m 32s
test (3.12)	3m 13s
check-links	54s
test (3.13-dev)	2m 46s
smoke (amaranth-lang/amaranth-soc)	43s
publish-docs	8s
publish-docs-dev	0s
required	3s
publish-package	11s
publish-schemas	7s
publish-release	0s
	39m 16s

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