gst_all_1: fix gst-python comment

pkgs/development/libraries/gstreamer/default.nix

···
     ipu6-camera-hal = ipu6ep-camera-hal;
   };
 
-  # note: gst-python is in ./python/default.nix - called under pythonPackages
+  # note: gst-python is in ../../python-modules/gst-python - called under python3Packages
 }