meson: Correctly require the Python.h header for the python dependency

meson: Correctly require the Python.h header for the python dependency

The current solution to require the Python.h header works around a bug
in Meson that has been fixed for version 1.4.1 of Meson.
Refer to https://github.com/mesonbuild/meson/issues/12862.
This change uses an explicit check for the Python.h include.
This verifies the required header exists.
This check is only necessary prior to version 1.4.1 of Meson.

Signed-off-by: Jordan Williams <jordan@jwillikers.com>