gh-117928: Bump the minimum Sphinx version to 6.2.1 #110203

Job	Run time
Check for source changes	10s
Check if generated files are up to date	5m 2s
Address sanitizer	8m 2s
Ubuntu SSL tests with OpenSSL (1.1.1w)	2m 14s
Ubuntu SSL tests with OpenSSL (3.0.13)	2m 12s
CIFuzz	0s
Ubuntu SSL tests with OpenSSL (3.1.5)	2m 24s
Hypothesis tests on Ubuntu	5m 42s
Ubuntu SSL tests with OpenSSL (3.2.1)	1m 55s
Windows / build and test (x64)	15m 37s
Windows / build (arm64)	3m 11s
Windows / build and test (x86)	15m 21s
macOS / build and test (macos-14)	9m 46s
macOS (free-threading) / build and test (macos-14)	7m 54s
macOS / build and test (macos-13)	8m 35s
Ubuntu / build and test	7m 33s
Windows (free-threading) / build and test (x64)	31m 13s
Windows (free-threading) / build and test (x86)	29m 30s
Thread sanitizer / Thread sanitizer	4m 27s
Thread sanitizer (free-threading) / Thread sanitizer	7m 5s
Ubuntu (free-threading) / build and test	9m 47s
WASI / build and test	11m 12s
Windows (free-threading) / build (arm64)	2m 21s
Docs / Docs	1m 56s
Docs / Docs (Oldest Sphinx)	2m 8s
Docs / Doctest	17m 7s
All required checks pass	3s
	3h 32m 27s

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