Posts, Post Types: Pass correct variable to the `get_lastpostdate` filter.

Follow-up to [48634].

See #49572.

git-svn-id: https://develop.svn.wordpress.org/trunk@48635 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/post.php

@@ -6634,7 +6634,7 @@ function get_lastpostdate( $timezone = 'server', $post_type = 'any' ) {
 	 *                                   See get_lastpostdate() for accepted `$timezone` values.
 	 * @param string       $post_type    The post type to check.
 	 */
-	return apply_filters( 'get_lastpostdate', $date, $timezone, $post_type );
+	return apply_filters( 'get_lastpostdate', $lastpostdate, $timezone, $post_type );
 }
 
 /**