expat: update to 2.6.2.

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!! <blink>Expat is UNDERSTAFFED and WITHOUT FUNDING.</blink>                !!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Release 2.6.2 Wed March 13 2024
        Security fixes:
      #839 #842  CVE-2024-28757 -- Prevent billion laughs attacks with
                    isolated use of external parsers.  Please see the commit
                    message of commit 1d50b80cf31de87750103656f6eb693746854aa8
                    for details.

        Bug fixes:
      #839 #841  Reject direct parameter entity recursion
                    and avoid the related undefined behavior

        Other changes:
            #847  Autotools: Fix build for DOCBOOK_TO_MAN containing spaces
            #837  Add missing #821 and #824 to 2.6.1 change log
      #838 #843  Version info bumped from 10:1:9 (libexpat*.so.1.9.1)
                    to 10:2:9 (libexpat*.so.1.9.2); see https://verbump.de/
                    for what these numbers do

        Special thanks to:
            Philippe Antoine
            Tomas Korbar
                and
            Clang UndefinedBehaviorSanitizer
            OSS-Fuzz / ClusterFuzz

(wiz)