fix(transport): return GDU for all errors from MDS universe_domain

refs: #2399

internal/settings.go

@@ -195,7 +195,7 @@ func (ds *DialSettings) IsUniverseDomainGDU() bool {
 // GetUniverseDomain returns the default service domain for a given Cloud
 // universe, from google.Credentials, for comparison with the value returned by
 // (*DialSettings).GetUniverseDomain. This wrapper function should be removed
-// to close [TODO(chrisdsmith): issue link here]. See details below.
+// to close https://github.com/googleapis/google-api-go-client/issues/2399.
 func GetUniverseDomain(creds *google.Credentials) (string, error) {
 	timer := time.NewTimer(time.Second)
 	defer timer.Stop()
@@ -212,9 +212,10 @@ func GetUniverseDomain(creds *google.Credentials) (string, error) {
 	}()
 
 	select {
-	case err := <-errors:
-		// An error that is returned before the timer expires is legitimate.
-		return "", err
+	case <-errors:
+		// An error that is returned before the timer expires is likely to be
+		// connection refused. Temporarily (2024-03-21) return the GDU domain.
+		return universeDomainDefault, nil
 	case res := <-results:
 		return res, nil
 	case <-timer.C: // Timer is expired.