Bump temporal SDK to 1.21.0 #1036

Job	Run time
build-lint-test (3.10, macos-arm)	7m 21s
build-lint-test (3.14, macos-intel)	17m 42s
build-lint-test (3.10, macos-intel)	10m 35s
build-lint-test (3.14, ubuntu-latest)	16m 1s
build-lint-test (3.14, macos-arm)	13m 15s
build-lint-test (3.10, windows-latest)	6m 25s
build-lint-test (3.14, windows-latest)	19m 38s
build-lint-test (3.10, ubuntu-latest)	5m 49s
	1h 36m 46s

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