quartz: fix compilation problem introduced by !5648
Including plain "gdkquartz.h" ends with compilation error:
../gtk/gtkfilechoosernativequartz.c:43:10: fatal error: 'gdkquartz.h' file not found
#include "gdkquartz.h"
^~~~~~~~~~~~~
1 error generated.
I had a look at how "gdkquartz.h" is included in other files and saw both "gdk/quartz/gdkquartz.h" and "quartz/gdkquartz.h" both of which fix this problem. I used the first path but I can change the patch to the second if it's preferred.