gnulib-tool: Simplify the Python version test. Suggested by Pádraig Brady in <https://lists.gnu.org/archive/html/bug-gnulib/2024-04/msg00469.html>. * gnulib-tool: Use Python's sys.version_info, not --version. * gnulib-tool.py: Use the same version test here. Use --version only to produce a specific error message.