Fix RST issues

Author: javiereguiluz

src/TwigComponent/doc/index.rst

@@ -461,7 +461,7 @@ passed when rendering the component.
 
 For example, if you call your component like this:
 
-.. code-block:: twig
+.. code-block:: html+twig
 
     <twig:Alert type="error" message="..."/>
 
@@ -509,7 +509,7 @@ Instead, define the values you need in the ``mount()`` method as arguments::
 
 Now, pass the ``mount()`` argument like any other prop:
 
-.. code-block:: twig
+.. code-block:: html+twig
 
     <twig:Alert isError="{{ true }}" message="..."/>