Fix: 2D Animation Template: Update Factory Startup

The function was iterating over the legacy ID type.
Use `bpy.data.grease_pencils_v3` instead.

scripts/startup/bl_app_templates_system/2D_Animation/__init__.py

@@ -37,8 +37,8 @@ def update_factory_startup_scenes():
 
 
 def update_factory_startup_grease_pencils():
-    for gpd in bpy.data.grease_pencils:
-        gpd.onion_keyframe_type = 'ALL'
+    for grease_pencil in bpy.data.grease_pencils_v3:
+        grease_pencil.onion_keyframe_type = 'ALL'
 
 
 @persistent