Media: Use correct option name for attachment pages in upgrade_640().

Follow-up to [56657].

See #57913.

git-svn-id: https://develop.svn.wordpress.org/trunk@56658 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/upgrade.php

@@ -2339,7 +2339,7 @@ function upgrade_640() {
 
 	if ( $wp_current_db_version < 56657 ) {
 		// Enable attachment pages.
-		update_option( 'wp_media_use_attachment_pages', 1 );
+		update_option( 'wp_attachment_pages_enabled', 1 );
 	}
 }