gh-144363: Update bundled libexpat to 2.7.4 (#144365)

* Update to 2.7.4

* update expat license copyright year to match and a pedantic #define

* include COPYING update in refresh.sh

* Update checksum for copying

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Co-authored-by: Gregory P. Smith <greg@krypto.org>
Co-authored-by: Petr Viktorin <encukou@gmail.com>