Don't fix Python version in .pre-commit-config.yaml

[elcorto]

We have

mala/.pre-commit-config.yaml

Lines 8 to 13 in 0fed9cc

	- id: black
	# It is recommended to specify the latest version of Python
	# supported by your project here, or alternatively use
	# pre-commit's default_language_version, see
	# https://pre-commit.com/#top_level-default_language_version
	language_version: python3.12

but on a system with only Python 3.11 available, we get

$ pre-commit run -a
An unexpected error has occurred: CalledProcessError: command: ('/path/to/python/3.11.2/bin/python3.11', '-mvirtualenv', '/home/user42/.cache/pre-commit/repokdlvjmqs/py_env-python3.12', '-p', 'python3.12')
return code: 1
stdout:
    RuntimeError: failed to find interpreter for Builtin discover of python_spec='python3.12'
stderr: (none)

We could also set this to python3.11, but I guess the more portable way is to rely on black's auto-detection and remove that setting.

[RandomDefaultUser]

I agree that as long as we don't enforce a python version across MALA (and maybe even then?) we shouldn't enforce a specific version here. Thanks for the PR!