[type:release] add release note #21

Job	Run time
build-and-test (x86_64-unknown-linux-gnu, stable)	5m 57s
build-and-test (x86_64-unknown-linux-gnu, nightly)	5m 57s
build-and-test (x86_64-apple-darwin, stable)	4m 44s
build-and-test (x86_64-apple-darwin, nightly)	5m 2s
build-and-test (aarch64-apple-darwin, stable)	5m 35s
build-and-test (aarch64-apple-darwin, nightly)	4m 47s
build-and-test (x86_64-pc-windows-gnu, stable)	15m 1s
build-and-test (x86_64-pc-windows-gnu, nightly)	13m 36s
build-and-test (i686-pc-windows-gnu, stable)	16m 10s
build-and-test (i686-pc-windows-gnu, nightly)	15m 52s
build-and-test (x86_64-pc-windows-msvc, stable)	13m 34s
build-and-test (x86_64-pc-windows-msvc, nightly)	13m 19s
build-and-test (i686-pc-windows-msvc, stable)	17m 12s
build-and-test (i686-pc-windows-msvc, nightly)	14m 25s
	2h 31m 11s

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