[3.10] gh-145506: Fixes CVE-2026-2297 by ensuring SourcelessFileLoader uses io.open_c...

[3.10] gh-145506: Fixes CVE-2026-2297 by ensuring SourcelessFileLoader uses io.open_code (GH-145507) (#145516)

* gh-145506: Fixes CVE-2026-2297 by ensuring SourcelessFileLoader uses io.open_code (GH-145507)
(cherry picked from commit a51b1b512de1d56b3714b65628a2eae2b07e535e)

Co-authored-by: Steve Dower <steve.dower@python.org>
* Regenerate importlib_external.h

* Fix blurb entry

The `:cve:` role is not available on this branch.

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Co-authored-by: Steve Dower <steve.dower@python.org>
Co-authored-by: Stan Ulbrych <stan@ulbrych.org>
Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>