minor #11137 use :: instead of .. code-block:: php (OskarStark)

This PR was merged into the 3.4 branch.

Discussion
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use :: instead of .. code-block:: php

and removed php open tag

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Commits
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ffabe90 use :: instead of .. code-block:: php

Author: javiereguiluz

bundles/best_practices.rst

@@ -265,11 +265,8 @@ following standardized instructions in your ``README.md`` file.
         -------------------------
 
         Then, enable the bundle by adding it to the list of registered bundles
-        in the ``app/AppKernel.php`` file of your project:
+        in the ``app/AppKernel.php`` file of your project::
 
-        .. code-block:: php
-
-            <?php
             // app/AppKernel.php
 
             // ...