bug #11251 Fix template name reference (stoccc)

This PR was merged into the 4.2 branch.

Discussion
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Fix template name reference

As written here https://symfony.com/doc/current/templating.html#referencing-templates-in-a-bundle
it seems that `{% extends "@!FOSUserBundle/Registration/confirmed.html.twig" %}` is not correct.

> @AcmeBlog/Blog/index.html.twig: This syntax is used to specify a template for a specific page. The three parts of the string, each
> separated by a slash (/), mean the following:
>
>    @AcmeBlog: is the bundle name **without** the Bundle suffix. This template lives in the AcmeBlogBundle (e.g. src/Acme/BlogBundle);

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Commits
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2511d35 Fix template reference

Author: wouterj

bundles/override.rst

@@ -45,7 +45,7 @@ extend from the original template, not from the overridden one:
 
     {# templates/bundles/FOSUserBundle/Registration/confirmed.html.twig #}
     {# the special '!' prefix avoids errors when extending from an overridden template #}
-    {% extends "@!FOSUserBundle/Registration/confirmed.html.twig" %}
+    {% extends "@!FOSUser/Registration/confirmed.html.twig" %}
 
     {% block some_block %}
         ...