minor #9712 Fix correct extension in comment of example (lex111)

This PR was submitted for the 4.0 branch but it was merged into the 2.7 branch instead (closes #9712).

Discussion
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Fix correct extension in comment of example

Because this is a PHP template (`html+php`), then the extension should be PHP.

Commits
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d005898 Fix correct extension in comment of example

Author: javiereguiluz

controller/upload_file.rst

@@ -102,7 +102,7 @@ to :doc:`customize form rendering </form/form_customization>`):
 
     .. code-block:: html+php
 
-        <!-- app/Resources/views/product/new.html.twig -->
+        <!-- app/Resources/views/product/new.html.php -->
         <h1>Adding a new product</h1>
 
         <?php echo $view['form']->start($form) ?>