Fix code style: double quotes instead of single quotes

CURA-4186

cura/Settings/PerObjectContainerStack.py

@@ -34,13 +34,13 @@ class PerObjectContainerStack(ContainerStack):
         # limit_to_extruder, so the values retrieved will be from the perspective of the original limit_to_extruder
         # stack.
         if limit_to_extruder == "-1":
-            if 'original_limit_to_extruder' in context.context:
-                limit_to_extruder = context.context['original_limit_to_extruder']
+            if "original_limit_to_extruder" in context.context:
+                limit_to_extruder = context.context["original_limit_to_extruder"]
 
         if limit_to_extruder is not None and limit_to_extruder != "-1" and limit_to_extruder in global_stack.extruders:
             # set the original limit_to_extruder if this is the first stack that has a non-overriden limit_to_extruder
-            if 'original_limit_to_extruder' not in context.context:
-                context.context['original_limit_to_extruder'] = limit_to_extruder
+            if "original_limit_to_extruder" not in context.context:
+                context.context["original_limit_to_extruder"] = limit_to_extruder
 
             if super().getProperty(key, "settable_per_extruder", context):
                 result = global_stack.extruders[str(limit_to_extruder)].getProperty(key, property_name, context)