T2295: fix CI failures (changelog line length, devel/py3.12 matrix)
Shorten the changelog fragment to satisfy ansible-lint line-length (160).
Skip py3.12-devel tox environments and exclude devel+Python 3.12 from
unit-source now that ansible-core devel requires Python >=3.13.
Co-authored-by: Cursor <cursoragent@cursor.com>