Add an <optgroup> to Gravity Forms "Bulk action" dropdown using GravityView.

gravityview-modify-optgroup.php

<?php
/**
 * Requires GravityView 1.16.3 or newer
 */

add_filter( 'gravityview/approve_entries/bulk_actions', 'gv_approve_entries_bulk_actions_pizzafy', 10, 2 );

/**
 * Add an <optgroup> to Gravity Forms "Bulk action" dropdown using GravityView.
 * 
 * @param array $bulk_actions Associative array of actions to be added to "Bulk action" dropdown inside GravityView `<optgroup>`. Parent array key is the `<optgroup>` label, then each child array must have `label` (displayed text) and `value` (input value) keys. Values get sanitized by GV.
 * @param int $form_id ID of the form currently being displayed
 * 
 * @return array Bulk actions, with map
 */
function gv_approve_entries_bulk_actions_pizzafy( $bulk_actions = array(), $form_id = 0 ) {

	$bulk_actions['GF Pizza-Pie'] = array(
		array(
			'label' => __( 'Send Free Pizzas', 'gravityview' ),
			'value' => sprintf( 'pizzafy-%d', $form_id ),
		),
	);

	return $bulk_actions;
}