FIX add static

src/caosdb/common/models.py

@@ -2580,6 +2580,7 @@ class Messages(list):
 
         super().append(msg)
 
+    @staticmethod
     def _hash(t, c):
         return hash(str(t).lower() + (str(",") + str(c) if c is not None else ''))
     # end remove