[3.13] gh-144984: Fix crash in Expat's `ExternalEntityParserCreate` error paths (GH-144992) (#146142)

* gh-144984: Fix crash in Expat's `ExternalEntityParserCreate` error paths (#144992)

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

* gh-144984: Skip test under tracerefs (GH-146218)

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Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
Co-authored-by: Petr Viktorin <encukou@gmail.com>