BPY types: add default Geometry Node poll function

Contrary to `CompositorNodeCustomGroup` or `ShaderNodeCustomGroup`,
`GeometryNodeCustomGroups` have to define their own poll function.
This is because their is no predefined poll function for `GeometryNode`,
and it may not be clear for addon developers why `GeometryNode` would
be special here.

This adds `GeometryNode` to `bpy_types.py` and defines such a function
for it like for other builtin node types.

Differential Revision: https://developer.blender.org/D14775

release/scripts/modules/bpy_types.py

@@ -1145,3 +1145,11 @@ class TextureNode(NodeInternal):
     @classmethod
     def poll(cls, ntree):
         return ntree.bl_idname == 'TextureNodeTree'
+
+
+class GeometryNode(NodeInternal):
+    __slots__ = ()
+
+    @classmethod
+    def poll(cls, ntree):
+        return ntree.bl_idname == 'GeometryNodeTree'