Bug report

Bug description:

Hello! 👋

(Once the upgrade to Expat 2.7.2 is complete at#138998) please upgrade bundled Expat to 2.7.3 (e.g. for two key bugfixes).

• GitHub release:https://github.com/libexpat/libexpat/releases/tag/R_2_7_3
• Change log:https://github.com/libexpat/libexpat/blob/R_2_7_3/expat/Changes

The CPython issue for previous 2.7.2 was#138998 and the related merged main pull request was#138999, in case you want to have a look. (TheDockerfile from comment#123689 (review) could be of help with raising confidence in a bump pull request when going forward.)

Thanks in advance!

CC@gpshead@StanFromIreland

CPython versions tested on:

3.9, 3.10, 3.11, 3.12, 3.13, 3.14, 3.15, CPython main branch

Operating systems tested on:

Linux, macOS, Windows, Other

Linked PRs

• gh-139312: Update bundled libexpat to 2.7.3 #139319
• [3.14] gh-139312: Update bundled libexpat to 2.7.3 (GH-139319) #139376
• [3.12] gh-139312: Update bundled libexpat to 2.7.3 (GH-139319) #139662
• [3.13] gh-139312: Update bundled libexpat to 2.7.3 (GH-139319) #139377
• [3.11] gh-139312: Update bundled libexpat to 2.7.3 (GH-139319) #139378
• [3.10] gh-139312: Update bundled libexpat to 2.7.3 (GH-139319) #139379
• [3.9] gh-139312: Update bundled libexpat to 2.7.3 (GH-139319) #139697