Reassign points value instead of updating when changing quality control

The value of points is an immutable dictionary that can not be updated.

Closes #13730
(grafted from d8119a6255ea750c4f4d9c4f54ba1485270012b0)

--HG--
branch : 7.0

modules/quality/quality.py

@@ -437,10 +437,10 @@ class Inspection(Workflow, ModelSQL, ModelView):
     @fields.depends('control', 'points')
     def on_change_control(self):
         if self.control:
-            if self.points is None:
-                self.points = {}
-            self.points.update(
+            points = dict(self.points) if self.points is not None else {}
+            points.update(
                 (p.name, None) for p in self.control.points)
+            self.points = points
 
     def validate_points(self):
         points = {p.name: p.string for p in self.control.points}