Bump version to v0.21.3 #11441

Job	Run time
build_node (ubuntu-latest)	1m 15s
build_node (macos-latest)	1m 32s
build_node (windows-latest)	6m 11s
Ruby 3.1 on ubuntu-latest	18m 51s
Ruby 3.2 on ubuntu-latest	16m 0s
lint_node	31s
Ruby 3.3 on ubuntu-latest	12m 33s
Ruby 3.1 on macos-latest	12m 39s
Ruby 3.2 on macos-latest	8m 44s
lint_ruby	22s
Ruby 3.3 on macos-latest	6m 42s
Ruby 3.1 on windows-latest	25m 33s
spelling	17s
Ruby 3.2 on windows-latest	21m 30s
Ruby 3.3 on windows-latest	23m 38s
Verify Jekyll website builds	7s
	2h 36m 25s

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