Try "python" before "python3" in python-mode

Try "python" before "python3" in python-mode

Prefer whatever version of Python that "python" might point to; use
"python3" if it doesn't exist.  On recent versions of typical GNU/Linux
distributions, "python" either does not exist or it points to Python 3.
In (presumed rare) cases where "python" points to Python 2 instead,
users are now expected to manually customize these variables if they
want to use Python 3.

* lisp/progmodes/python.el (python-interpreter)
(python-shell-interpreter): Prefer "python" to "python3".

Ref:
https://lists.gnu.org/r/emacs-devel/2024-09/msg00885.html
(cherry picked from commit dd4c67907eb3084c6f55828c51bca1675a98376d)