The package needs porting to Python 3.13.
Fixed with commit edb9d35b6e837c4459354da3b40cee61276065a4 Author: Alexey Shvetsov <alexxy@gentoo.org> Date: Wed Apr 2 12:09:49 2025 +0300 dev-python/sphinx-copybutton: enable py3.13 Signed-off-by: Alexey Shvetsov <alexxy@gentoo.org>