Fix broken quotes.

PiperOrigin-RevId: 446496649

Author: MarkDaoust

site/en/community/contribute/docs_ref.md

@@ -100,15 +100,15 @@ TensorFlow uses a few customizations to the builtin doctest logic:
 
     ```
     def NewLayer():
-      “””This layer does cool stuff.
+      """This layer does cool stuff.
 
       Example usage:
 
       >>> x = tf.random.normal((1, 28, 28, 3))
       >>> new_layer = NewLayer(x)
       >>> new_layer
       <tf.Tensor: shape=(1, 14, 14, 3), dtype=int32, numpy=...>
-      “””
+      """
     ```
 
 *   *Floating point values*: The TensorFlow doctest extracts float values from