pygi-argument: Fix a potentially misaligned cast
pygi-argument: Fix a potentially misaligned cast

The item size in the array does not strictly have the same alignment as
GIArgument so better memcpy to the stack first.

clang complained about this

GNOME/pygobject,pexip/pygobject,pexip/pygobject,GNOME/pygobject,GNOME/pygobject,pexip/pygobject