Update layer.py add_loss to properly handle when input loss is a list of scalar tensor (#21291)

Author: franklin5

keras/src/layers/layer.py

@@ -1203,8 +1203,8 @@ def call(self, x):
             scope = backend.get_stateless_scope()
             if scope.collect_losses:
                 for x in losses:
-                    scope.add_loss(loss)
-                    self._loss_ids.add(id(loss))
+                    scope.add_loss(x)
+                    self._loss_ids.add(id(x))
         else:
             self._losses.extend(losses)