gh-123678: Upgrade libexpat 2.6.3 #124382

Job	Run time
Change detection / Compute changed files	11s
Check if generated files are up to date	5m 32s
Ubuntu SSL tests with OpenSSL (1.1.1w)	2m 25s
Ubuntu SSL tests with OpenSSL (3.0.13)	2m 19s
Ubuntu SSL tests with OpenSSL (3.1.5)	2m 41s
Ubuntu SSL tests with OpenSSL (3.2.1)	2m 18s
Windows MSI${{ '' }}	0s
Address sanitizer	7m 35s
CIFuzz (address)	20m 12s
Hypothesis tests on Ubuntu	5m 39s
CIFuzz (undefined)	20m 58s
CIFuzz (memory)	20m 54s
Thread sanitizer / Thread sanitizer	5m 39s
Thread sanitizer (free-threading) / Thread sanitizer	7m 47s
WASI / build and test	7m 25s
macOS (free-threading) / build and test (ghcr.io/cirruslabs/macos-runner:sonoma)	5m 21s
macOS / build and test (ghcr.io/cirruslabs/macos-runner:sonoma)	4m 40s
macOS / build and test (macos-13)	11m 24s
Ubuntu / build and test	7m 24s
Ubuntu (free-threading) / build and test	10m 4s
Windows / build (arm64)	3m 5s
Windows (free-threading) / build (arm64)	3m 5s
Windows / build and test (Win32)	16m 27s
Windows (free-threading) / build and test (Win32)	24m 24s
Windows / build and test (x64)	17m 35s
Windows (free-threading) / build and test (x64)	22m 42s
Docs / Docs	2m 0s
Docs / Docs (Oldest Sphinx)	2m 9s
Docs / Doctest	20m 23s
All required checks pass	4s
	4h 22m 22s

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