gobject-introspection: inherit python3targetconfig

gobject-introspection: inherit python3targetconfig

When building gobject-introspection for aarch64, the generated giscanner
python module has the wrong "x86_64" suffix:
./usr/lib/gobject-introspection/giscanner/_giscanner.cpython-311-x86_64-linux-gnu.so

The EXT_SUFFIX used by meson to generate the python module is taken
from the native python3 sysconfig instead of the target sysconfig.

Replace the python3native inherit with python3targetconfig to fix this.

Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>