Fix trailing comma

Co-authored-by: Copilot <[email protected]>

Author: dlh01

src/match-blocks.php

@@ -174,7 +174,7 @@ function match_blocks( $source, $args = [] ) {
 			],
 		);
 
-		$xml_content   = $serializer->serialize( Blocks::from_parsed_blocks( $blocks ), 'xml', );
+		$xml_content   = $serializer->serialize( Blocks::from_parsed_blocks( $blocks ), 'xml' );
 		$xml_element   = new SimpleXMLElement( $xml_content );
 		$xpath_matches = $xml_element->xpath( $args['__experimental_xpath'] );