minor #15545 [Form] Remove useless quotes for render_rest attribute (welcoMattic)

This PR was submitted for the 5.4 branch but it was merged into the 4.4 branch instead.

Discussion
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[Form] Remove useless quotes for `render_rest` attribute

Quotes are useless here, it's clearer without

Commits
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64b2d45 Remove useless quotes for `render_rest` attribute

Author: javiereguiluz

form/form_customization.rst

@@ -204,7 +204,7 @@ article) unless you set ``render_rest`` to false:
 .. code-block:: twig
 
     {# don't render unrendered fields #}
-    {{ form_end(form, {'render_rest': false}) }}
+    {{ form_end(form, {render_rest: false}) }}
 
 .. _reference-forms-twig-label: