[3.13] gh-121188: Sanitize invalid XML characters in regrtest (GH-121195) (#121204)

gh-121188: Sanitize invalid XML characters in regrtest (GH-121195)

When creating the JUnit XML file, regrtest now escapes characters
which are invalid in XML, such as the chr(27) control character used
in ANSI escape sequences.
(cherry picked from commit af8c3d7a26d605099f5b3406a8d33ecddb77e8fb)

Co-authored-by: Victor Stinner <vstinner@python.org>