Gravity Forms: Add Surrogate-Control header if Gravity Form is present on page

gf-surrogate-control-header.php

<?php
/**
 * Set Surrogate-Control header on pages with Gravity Forms to prevent Varnish from caching.
 *
 * This requires Varnish to be configured to utilize Surrogate-Control when present.
 *
 * See the follow material for more details:
 *     * https://developer.fastly.com/reference/http-headers/Surrogate-Control/
 *     * https://book.varnish-software.com/4.0/chapters/VCL_Basics.html#vcl-backend-response
 */
add_action( 'gform_post_enqueue_scripts', function ( $forms ) {
	// If HTTP headers have already been sent, we can't modify them.
	if ( headers_sent() ) {
		return;
	}

	header( 'Surrogate-Control: no-store' );
} );