net: mark tests with retry as parallel

Fixes #24580

Change-Id: I7536aca1e90717283bd6a3bb4b1bab059b0cf720
Reviewed-on: https://go-review.googlesource.com/104677
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/lookup_test.go

@@ -63,6 +63,7 @@ var lookupGoogleSRVTests = []struct {
 var backoffDuration = [...]time.Duration{time.Second, 5 * time.Second, 30 * time.Second}
 
 func TestLookupGoogleSRV(t *testing.T) {
+	t.Parallel()
 	if testenv.Builder() == "" {
 		testenv.MustHaveExternalNetwork(t)
 	}
@@ -109,6 +110,7 @@ var lookupGmailMXTests = []struct {
 }
 
 func TestLookupGmailMX(t *testing.T) {
+	t.Parallel()
 	if testenv.Builder() == "" {
 		testenv.MustHaveExternalNetwork(t)
 	}
@@ -117,8 +119,6 @@ func TestLookupGmailMX(t *testing.T) {
 		t.Skip("IPv4 is required")
 	}
 
-	defer dnsWaitGroup.Wait()
-
 	attempts := 0
 	for i := 0; i < len(lookupGmailMXTests); i++ {
 		tt := lookupGmailMXTests[i]
@@ -189,6 +189,7 @@ var lookupGmailTXTTests = []struct {
 }
 
 func TestLookupGmailTXT(t *testing.T) {
+	t.Parallel()
 	if testenv.Builder() == "" {
 		testenv.MustHaveExternalNetwork(t)
 	}
@@ -197,8 +198,6 @@ func TestLookupGmailTXT(t *testing.T) {
 		t.Skip("IPv4 is required")
 	}
 
-	defer dnsWaitGroup.Wait()
-
 	attempts := 0
 	for i := 0; i < len(lookupGmailTXTTests); i++ {
 		tt := lookupGmailTXTTests[i]