fix: proxy-groups filter logic

adapter/outboundgroup/urltest.go

@@ -35,6 +35,10 @@ type URLTest struct {
 	failedTime  *atomic.Int64
 }
 
+func (u *URLTest) IsProxyGroup() bool {
+	return true
+}
+
 func (u *URLTest) Now() string {
 	return u.fast(false).Name()
 }