Avoid changing constant state of POIs during workspace modification

Allow setting unconstrained NPs as POIs

quickstats/components/workspaces/xml_ws_modifier.py

@@ -611,7 +611,7 @@ class XMLWSModifier(XMLWSBase):
                 self.stdout.warning(f"The nuisance parameter {nuis_name} no longer exists in "
                                     "the new workspace. It will be removed from the new ModelConfig.")
                 continue
-            if nuis.isConstant():
+            if nuis.isConstant() and nuis not in pois:
                 self.stdout.warning(f"The nuisace parameter {nuis_name} is initialized as a constant. "
                                     "It will be floated in the new workspace.")
                 nuis.setConstant(False)