fix: routinegroup & etcd watch goroutine leak (#4514)

Co-authored-by: Kevin Wan <wanjunfeng@gmail.com>

core/discov/subscriber_test.go

@@ -214,6 +214,18 @@ func TestSubscriber(t *testing.T) {
 	assert.Equal(t, int32(1), atomic.LoadInt32(&count))
 }
 
+func TestSubscriberClos(t *testing.T) {
+	l := newContainer(false)
+	sub := &Subscriber{
+		endpoints: []string{"localhost:2379"},
+		key:       "foo",
+		items:     l,
+	}
+	_ = internal.GetRegistry().Monitor(sub.endpoints, sub.key, l, false)
+	sub.Close()
+	assert.Empty(t, sub.items.listeners)
+}
+
 func TestWithSubEtcdAccount(t *testing.T) {
 	endpoints := []string{"localhost:2379"}
 	user := stringx.Rand()