tools: Fix missing cursor for MyPaint Brush tool

Resolves #15001
In the MyPaint Brushes v2 port (ea8b9dc1),
I implemented a cursor_update () function from the
parent class. However, I did not call the parent's
version of the function afterwards, so the MyPaint
Brush cursor was not being redrawn. This patch
adds the call to fix the cursor display issue.

app/tools/gimpmybrushtool.c

@@ -127,6 +127,8 @@ static void gimp_mybrush_tool_cursor_update (GimpTool         *tool,
   options->view_zoom     = (gimp_zoom_model_get_factor (shell->zoom) > 0.0f) ?
                             gimp_zoom_model_get_factor (shell->zoom) : 1.0f;
   options->view_rotation = shell->rotate_angle;
+
+  GIMP_TOOL_CLASS (parent_class)->cursor_update (tool, coords, state, display);
 }
 
 static void