[gardening] fix retries in socket_ipv6_test

Change-Id: Iaf7c7127896b99f69eec7b0f68328874490356cd
Reviewed-on: https://dart-review.googlesource.com/c/84035
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Daco Harkes <dacoharkes@google.com>
diff --git a/tests/standalone_2/io/socket_ipv6_test.dart b/tests/standalone_2/io/socket_ipv6_test.dart
index 769506f..4fb14cd 100644
--- a/tests/standalone_2/io/socket_ipv6_test.dart
+++ b/tests/standalone_2/io/socket_ipv6_test.dart
@@ -130,6 +130,7 @@
 }
 
 main() async {
+  asyncStart();
   await testIPv6toIPv6(); //               //# 01: ok
   await testIPv4toIPv6(); //               //# 02: ok
   await testIPv4toIPv4(); //               //# 03: ok
@@ -138,4 +139,5 @@
 
   await retry(testIPv6toIPv4); //          //# 06: ok
   await retry(testIPv4toIPv6_IPV6Only); // //# 07: ok
+  asyncEnd();
 }