expat: Update to version 2.7.3

expat: Update to version 2.7.3

- Update from version 2.7.2 to 2.7.3
- Update of rootfile
- Changelog
    2.7.3
	Security fixes:
	      Fix alignment of internal allocations for some non-amd64
	       architectures (e.g. sparc32); fixes up on the fix to
	        CVE-2025-59375 from #1034 (of Expat 2.7.2 and related
	        backports)
	      Fix a class of false positives where input should have been
	       rejected with error XML_ERROR_ASYNC_ENTITY; regression from
	       CVE-2024-8176 fix pull request #973 (of Expat 2.7.0 and
	       related backports). Please check the added unit tests for
	       example documents.
	Other changes:
	       Prove and regression-proof absence of integer overflow
	        from function expat_realloc
	       Remove "harmless" cast that truncated a size_t to unsigned
	       Autotools: Remove "ln -s" discovery
	       docs: Be consistent with use of floating point around
	        XML_SetAllocTrackerMaximumAmplification
	       docs: Make it explicit that XML_GetCurrentColumnNumber starts at 0
	       docs: Better integrate the effect of the activation thresholds
	       docs: Fix an in-comment typo in expat.h
	       docs: Fix a typo in README.md
	       docs: Improve change log of release 2.7.2
	       xmlwf: Resolve use of functions XML_GetErrorLineNumber
	        and XML_GetErrorColumnNumber
	       Windows: Normalize .bat files to CRLF line endings
	       Version info bumped from 12:0:11 (libexpat*.so.1.11.0)
	        to 12:1:11 (libexpat*.so.1.11.1); see https://verbump.de/
	        for what these numbers do
	Infrastructure:
	       CI: Cleanup UndefinedBehaviorSanitizer fatality
	       CI|Linux: Stop aborting at first job failure
	       CI|FreeBSD: Upgrade to FreeBSD 15.0
	       CI|FreeBSD: Do not install CMake meta-package

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>