[11.x] Passes the application instance to withRouting's then callable. (#49654)

Author: lukeraymonddowning

src/Illuminate/Foundation/Configuration/ApplicationBuilder.php

@@ -176,7 +176,7 @@ class_exists(Folio::class)) {
             }
 
             if (is_callable($then)) {
-                $then();
+                $then($this->app);
             }
         };
     }