minor #20165 [Serializer] add missing use statement (xabbuh)

This PR was merged into the 5.4 branch.

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[Serializer] add missing use statement

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d0f46a2 add missing use statement

Author: javiereguiluz

components/serializer.rst

@@ -388,6 +388,7 @@ Then, create your groups definition:
 
 You are now able to serialize only attributes in the groups you want::
 
+    use Acme\MyObj;
     use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;
     use Symfony\Component\Serializer\Serializer;