package/libqrtr-glib: add gobject-introspection optional dependency

gobject-introspection is an optional dependency (enabled by default)
since the addition of the package in commit
ea64e05a

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Reviewed-by: Petr Vorel <petr.vorel@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>