GitHub Action CI: Add Go source file format check (#6090)

https://github.com/XTLS/Xray-core/pull/6057#issuecomment-4364819830

And https://github.com/XTLS/Xray-core/pull/6149#issuecomment-4546876261

app/router/router.go

@@ -110,7 +110,6 @@ func (r *Router) PickRoute(ctx routing.Context) (routing.Route, error) {
 
 // AddRule implements routing.Router.
 func (r *Router) AddRule(config *serial.TypedMessage, shouldAppend bool) error {
-
 	inst, err := config.GetInstance()
 	if err != nil {
 		return err
@@ -227,7 +226,6 @@ func (r *Router) RemoveRule(tag string) error {
 		return nil
 	}
 	return errors.New("empty tag name!")
-
 }
 
 // ListRule implements routing.Router