Fix: Error when baking custom properties of unavailable addon

When baking an Action on an object which has custom properties that come
from an addon or python script that isn't loaded, the baking would fail with:
```
TypeError: Cannot assign a 'dict' value to the existing 'hops' Group IDProperty
```

This comes from an addon that isn't present or loaded on a users machine.
The fix is to check for `IDProperty` and skip those.

Pull Request: https://projects.blender.org/blender/blender/pulls/129057

scripts/modules/bpy_extras/anim_utils.py

@@ -243,11 +243,14 @@ def bake_action_iter(
         return clean_props
 
     def bake_custom_properties(obj, *, custom_props, frame, group_name=""):
+        import idprop
         if frame is None or not custom_props:
             return
         for key, value in custom_props.items():
             if key in obj.bl_rna.properties and not obj.bl_rna.properties[key].is_animatable:
                 continue
+            if isinstance(obj[key], idprop.types.IDPropertyGroup):
+                continue
             obj[key] = value
             if key in obj.bl_rna.properties:
                 rna_path = key