Fix: Incorrect tool brush check for grease pencil vertex paint mode

This vertex paint code was just recently added in 942499382d, so the
property wasn't renamed correctly after b64bf66257 (which was created
earlier, just committed later).

scripts/startup/bl_ui/space_view3d.py

@@ -569,7 +569,7 @@ class _draw_tool_settings_context_mode:
 
     @staticmethod
     def VERTEX_GREASE_PENCIL(context, layout, tool):
-        if (tool is None) or (not tool.has_datablock):
+        if (tool is None) or (not tool.use_brushes):
             return False
 
         tool_settings = context.tool_settings