chore: fix warnings (#3990)

rest/engine_test.go

@@ -435,7 +435,7 @@ type mockedRouter struct {
 func (m mockedRouter) ServeHTTP(_ http.ResponseWriter, _ *http.Request) {
 }
 
-func (m mockedRouter) Handle(_, _ string, handler http.Handler) error {
+func (m mockedRouter) Handle(_, _ string, _ http.Handler) error {
 	return errors.New("foo")
 }