Update changelog for v3.28.21 #5164

Job	Run time
Ruby analysis (macos-latest, default)	1m 17s
Ruby analysis (ubuntu-latest, linked)	49s
Ruby analysis (ubuntu-latest, nightly-latest)	1m 5s
Ruby analysis (ubuntu-latest, default)	43s
Ruby analysis (macos-latest, linked)	1m 50s
Ruby analysis (macos-latest, nightly-latest)	2m 8s
	7m 52s

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