Adding _tie_weights() to prediction heads to support low_cpu_mem_usage=True (#29024)

* Adding _tie_weights() to prediction heads to support low_cpu_mem_usage=True

* Testing for the non-safe-tensors case, since the default is safe-tensors already

* Running fixup/fix-copies

* Adding accelerate annotations to tests

tests/models/deformable_detr/test_modeling_deformable_detr.py

@@ -578,6 +578,18 @@ class DeformableDetrModelTest(ModelTesterMixin, GenerationTesterMixin, PipelineT
                         msg=f"Parameter {name} of model {model_class} seems not properly initialized",
                     )
 
+    @unittest.skip("No support for low_cpu_mem_usage=True.")
+    def test_save_load_low_cpu_mem_usage(self):
+        pass
+
+    @unittest.skip("No support for low_cpu_mem_usage=True.")
+    def test_save_load_low_cpu_mem_usage_checkpoints(self):
+        pass
+
+    @unittest.skip("No support for low_cpu_mem_usage=True.")
+    def test_save_load_low_cpu_mem_usage_no_safetensors(self):
+        pass
+
     def test_two_stage_training(self):
         model_class = DeformableDetrForObjectDetection
         config, inputs_dict = self.model_tester.prepare_config_and_inputs_for_common()