[pre-commit] Stop using deprecated language script

In v4.4.0, pre-commit renamed language script to unsupported_script.

The rename was done to stress that pre-commit doesn't provide an environment
for the script to run in [1].

The language script is now a deprecated alias for unsupported_script, and the
plan seems to be to initially produce a deprecation warning, and eventually
remove support for the alias completely.

Start using the new name: unsupported_script.

Furthermore, the check-include-guards hook uses language python, and indeed it
uses a python script, but it doesn't really need a virtual environment.  It
imports modules fnmatch, re, sys and typing, all of which are available in
python 3.10 and later, which is the environment pre-commit itself requires
(because we require pre-commit v4.5.1 or later, and pre-commit requires python
3.10 since v4.4.0).  So while we're at it, use unsupported_script for this
hook as well, reducing the amount of environments pre-commit has to manage.

Tested using "pre-commit run --all-files" with python 3.10, as well as 3.13.

Approved-By: Simon Marchi <simon.marchi@efficios.com>

[1] https://github.com/pre-commit/pre-commit/pull/3577