[FIX] validation message on activity done button

activity_validation/models/mail_activity.py

@@ -249,13 +249,19 @@ def checkChildrenECODone(self, activity_id):
             raise UserError(_('You cannot move to Done because there are pending ECO activities.'))
 
     def checkChildrenECRDone(self, activity_id):
-        do_ecr = f"You cannot move to ECO or to Done because there are pending ECR activities for User:\n"
-        for child in activity_id.children_ids:
-            if child.plm_state not in ['done', 'cancel']:
-                do_ecr += f"\t-->\t{child.user_id.name}\n"
 
-        if do_ecr:
-            raise UserError(_(do_ecr))
+        pending_ecr_users = [
+            child.user_id.name
+            for child in activity_id.children_ids
+            if child.plm_state not in ['done', 'cancel']
+        ]
+        if pending_ecr_users:
+            user_list = "\n".join(f"\t-->\t{user}" for user in pending_ecr_users)
+            message = (
+                "You cannot move to ECO or to Done because there are pending ECR activities for User:\n"
+                f"{user_list}"
+            )
+            raise UserError(_(message))
 
     def action_to_eco(self):
         for activity_id in self: