[Cherry-pic]Fix the bug in fleet amp_init. (#30606) (#30608)

* Fix the bug in fleet amp_init.

* Fix the amp_init unit test.

Author: wzzju

python/paddle/distributed/fleet/base/fleet_base.py

@@ -1019,8 +1019,8 @@ def run_example_code():
                     run_example_code()       
         """
         # imitate target optimizer retrieval
-        return self.user_defined_optimizer.amp_init(
-            place, scope=None, test_program=None, use_fp16_test=False)
+        return self.user_defined_optimizer.amp_init(place, scope, test_program,
+                                                    use_fp16_test)
 
     def _final_strategy(self):
         if "valid_strategy" not in self._context:

python/paddle/fluid/tests/unittests/test_fleet_amp_init.py

@@ -67,7 +67,7 @@ def test_fleet_amp_init(self):
 
         exe = paddle.static.Executor(place)
         exe.run(paddle.static.default_startup_program())
-        optimizer.amp_init(place, use_fp16_test=True)
+        optimizer.amp_init(place)
 
         step = 1
         for i in range(step):