[Fix deprecation warning in test] np.float => np.float64 (#49970)

python/paddle/optimizer/lr.py

@@ -1406,7 +1406,7 @@ class ReduceOnPlateau(LRScheduler):
             metrics, (int, float, numpy.float32, numpy.float64)
         ):
             raise TypeError(
-                "metrics must be 'int', 'float', 'np.float', 'numpy.ndarray' or 'paddle.Tensor', but receive {}".format(
+                "metrics must be 'int', 'float', 'np.float64', 'numpy.ndarray' or 'paddle.Tensor', but receive {}".format(
                     type(metrics)
                 )
             )