python3Packages.django_4: fix geos_gdal patch syntax error

pkgs/development/python-modules/django/django_4_set_geos_gdal_lib.patch

···
      lib_path = settings.GDAL_LIBRARY_PATH
  except (AttributeError, ImportError, ImproperlyConfigured, OSError):
 -    lib_path = None
-+    lib_path = ""@gdal@/lib/libgdal@extension@"
++    lib_path = "@gdal@/lib/libgdal@extension@"
  
  if lib_path:
      lib_names = None