GH-114736: Use WASI SDK 21 #106042

Job	Run time
Check for source changes	9s
Check if generated files are up to date	6m 10s
Address sanitizer	7m 6s
Ubuntu SSL tests with OpenSSL (1.1.1w)	2m 41s
Ubuntu SSL tests with OpenSSL (3.0.13)	2m 16s
CIFuzz	0s
Ubuntu SSL tests with OpenSSL (3.1.5)	1m 55s
Hypothesis tests on Ubuntu	4m 29s
Ubuntu SSL tests with OpenSSL (3.2.1)	2m 10s
Windows (free-threading) / build and test (x64)	22m 25s
Windows (free-threading) / build (arm64)	3m 21s
Windows (free-threading) / build and test (x86)	24m 26s
macOS / build and test (macos-14)	7m 17s
macOS / build and test (macos-13)	8m 20s
macOS (free-threading) / build and test (macos-14)	11m 57s
macOS (free-threading) / build and test (macos-13)	13m 40s
Ubuntu / build and test	6m 32s
Ubuntu (free-threading) / build and test	8m 20s
Windows / build and test (x64)	14m 6s
Windows / build (arm64)	2m 24s
Windows / build and test (x86)	13m 44s
WASI / build and test	8m 40s
Docs / Docs (Oldest Sphinx)	1m 40s
Docs / Doctest	5m 56s
Docs / Docs	2m 0s
All required checks pass	3s
	3h 1m 47s

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