Issue #843: Sanitize $_GET value in addition to the 'ignore' comment.
Issue #843: Sanitize $_GET value in addition to the 'ignore' comment.

Use sanitize_text_field( wp_unslash() ).
WPCS still requires nonce verification.
But there is no nonce on this page.
This is using the 'edit_form_top' action.

ampproject/amp-toolbox-php,ampproject/amp-toolbox-php