minor #17327 [Serializer] Fix XML example of ignoring an attribute redux (likeuntomurphy)

This PR was merged into the 5.4 branch.

Discussion
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[Serializer] Fix XML example of ignoring an attribute redux

This effectively reopens #16824, which could not be reopened because of a rebase after the PR was closed.

Commits
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3c0734a Change 'ignore' element to attribute in Serializer XML example

Author: javiereguiluz

components/serializer.rst

@@ -517,9 +517,7 @@ Option 1: Using ``@Ignore`` Annotation
                 https://symfony.com/schema/dic/serializer-mapping/serializer-mapping-1.0.xsd"
         >
             <class name="App\Model\MyClass">
-                <attribute name="bar">
-                    <ignore>true</ignore>
-                </attribute>
+                <attribute name="bar" ignore="true"/>
             </class>
         </serializer>