SC2: Fix custom mission order if used in weights.yaml (#5604)

worlds/sc2/mission_order/options.py

@@ -176,8 +176,7 @@ class CustomMissionOrder(OptionDict):
         # This function constructs self.value by parts,
         # so the parent constructor isn't called
         self.value: Dict[str, Dict[str, Any]] = {}
-        if yaml_value == self.default: # If this option is default, it shouldn't mess with its own values
-            yaml_value = copy.deepcopy(self.default)
+        yaml_value = copy.deepcopy(yaml_value) # Ensure that all the mutations are local to the world
 
         for campaign in yaml_value:
             self.value[campaign] = {}