Prepare 21.2.1 release. #1460

Job	Run time
sdist	46s
ruff	6s
mypy	29s
parse_sdl (windows-latest, 3.2.16)	41s
parse_sdl (macos-latest, 3.2.16)	33s
test-docs	2m 6s
pyodide	2m 8s
tox (ubuntu-latest)	2m 1s
build-macos (pp311-*)	4m 1s
build-macos (cp314t-*_universal2)	2m 43s
linux-wheels (aarch64, cp310-manylinux*)	3m 58s
linux-wheels (x86_64, cp310-manylinux*)	4m 6s
build-macos (cp310-*_universal2)	2m 12s
linux-wheels (x86_64, pp311-manylinux*)	3m 53s
linux-wheels (aarch64, cp314t-manylinux*)	4m 3s
linux-wheels (aarch64, pp311-manylinux*)	3m 39s
linux-wheels (x86_64, cp314t-manylinux*)	4m 6s
build (ubuntu-latest, pypy-3.10, x64)	3m 25s
build (windows-11-arm, 3.11, arm64)	3m 57s
build (windows-latest, pypy-3.10, x64)	3m 33s
build (ubuntu-latest, 3.14t, x64)	3m 50s
build (windows-latest, 3.14t, x86)	4m 14s
build (windows-latest, 3.14t, x64)	3m 5s
build (windows-11-arm, 3.14t, arm64)	4m 9s
build (windows-latest, 3.10, x64)	2m 48s
build (windows-latest, 3.10, x86)	3m 29s
build (ubuntu-latest, 3.10, x64)	3m 38s
publish	1m 2s
	1h 18m 41s

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