Fix compat check for 6.6

Author: westonruter

plugins/web-worker-offloading/tests/test-web-worker-offloading.php

@@ -208,7 +208,7 @@ public function test_update_script_types( Closure $set_up, string $expected ): v
 
 		$normalize = static function ( $html ) {
 			// See <https://core.trac.wordpress.org/ticket/63887>.
-			if ( class_exists( 'WP_HTML_Tag_Processor' ) ) {
+			if ( method_exists( 'WP_HTML_Tag_Processor', 'set_modifiable_text' ) ) { // @phpstan-ignore function.alreadyNarrowedType
 				// This normalization logic is only relevant to WP>=6.9-alpha anyway.
 				$p = new WP_HTML_Tag_Processor( $html );
 				while ( $p->next_tag( array( 'tag_name' => 'SCRIPT' ) ) ) {