Upgrade bundled Expat to 2.7.2 (e.g. for the fix to CVE-2025-59375)

[hartwork]

Bug report

Bug description:

Hi! 👋

Please upgrade bundled Expat to 2.7.2 (e.g. for the fix to CVE-2025-59375).

• GitHub release: https://github.com/libexpat/libexpat/releases/tag/R_2_7_2
• Change log: https://github.com/libexpat/libexpat/blob/R_2_7_2/expat/Changes

The CPython issue for previous 2.7.1 was #131809 and the related merged main pull request was #132192, in case you want to have a look. (The Dockerfile from comment #123689 (review) could be of help with raising confidence in a bump pull request when going forward.)

Thanks in advance!

CC @sethmlarson @gpshead

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-138998: Upgrade vendored expat to 2.7.2 #138999
• [3.14] gh-138998: Upgrade vendored expat to 2.7.2 (GH-138999) #139024
• [3.13] gh-138998: Upgrade vendored expat to 2.7.2 (GH-138999) #139025
• [3.12] gh-138998: Upgrade vendored expat to 2.7.2 (GH-138999) #139026
• gh-138998: expat/refresh.sh: Fail if Step 3 is not completed #139049
• [3.10] gh-138998: Upgrade vendored expat to 2.7.2 (#138999) #139053
• [3.9] gh-138998: Upgrade vendored expat to 2.7.2 (GH-138999) #139055
• [3.11] gh-138998: Upgrade vendored expat to 2.7.2 (#138999) #139056