Updated keras.layers.activations.ReLU API with keras.layers.ReLU in E…

…xample from relu.py file (#20403)

`keras.layers.activations.ReLU API` throwing `AttributeError: module 'keras.api.layers' has no attribute 'activations'`.  Modified      it with`keras.layers.ReLU API.

keras/src/layers/activations/relu.py

@@ -17,7 +17,7 @@ class ReLU(Layer):
 
     Example:
     ``` python
-    relu_layer = keras.layers.activations.ReLU(
+    relu_layer = keras.layers.ReLU(
         max_value=10,
         negative_slope=0.5,
         threshold=0,