[Reference][Twig] Fix typos and formatting

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.2+
| Fixed tickets | -

The line numbers are missing for the Twig+HTML code block in `reference/forms/twig_reference.rst`. I hope this gets fixed by removing the line feed within the HTML tag. Please let me know if this needs to get fixed in a different way.