Update changelog for v3.28.21 #5182

Job	Run time
Ruby analysis (macos-latest, default)	1m 47s
Ruby analysis (ubuntu-latest, nightly-latest)	1m 9s
Ruby analysis (ubuntu-latest, default)	48s
Ruby analysis (ubuntu-latest, linked)	1m 1s
Ruby analysis (macos-latest, linked)	1m 48s
Ruby analysis (macos-latest, nightly-latest)	2m 1s
	8m 34s

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