docs(hooks): update comment_flood_message xref

Update cross-reference for comment_flood_message from
`comment-template.php` to `comment.php` where the
hook's PHPDoc block now lives.

Related to https://core.trac.wordpress.org/ticket/64224

Author: apermo

src/wp-includes/comment.php

@@ -807,7 +807,7 @@ function wp_allow_comment( $commentdata, $wp_error = false ) {
 	);
 
 	if ( $is_flood ) {
-		/** This filter is documented in wp-includes/comment-template.php */
+		/** This filter is documented in wp-includes/comment.php */
 		$comment_flood_message = apply_filters( 'comment_flood_message', __( 'You are posting comments too quickly. Slow down.' ) );
 
 		return new WP_Error( 'comment_flood', $comment_flood_message, 429 );