Fix backwards compatibility with WP_REST_Request API (WordPress#98)

Replace is_method() with get_method() for WordPress compatibility. The is_method() method does not exist on WP_REST_Request in earlier WordPress versions.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

Co-authored-by: budzanowski <budzanowski@git.wordpress.org>
Co-authored-by: gziolo <gziolo@git.wordpress.org>

Author: 3 people

includes/rest-api/endpoints/class-wp-rest-abilities-list-controller.php

@@ -105,7 +105,7 @@ public function get_items( $request ) {
 		$total_abilities = count( $abilities );
 		$max_pages       = ceil( $total_abilities / $per_page );
 
-		if ( $request->is_method( 'HEAD' ) ) {
+		if ( $request->get_method() === 'HEAD' ) {
 			$response = new \WP_REST_Response( array() );
 		} else {
 			$abilities = array_slice( $abilities, $offset, $per_page );