spanner: skip TestIntegration_StartBackupOperation

Updates #2393

Change-Id: I9edfa9c214f4448d2bf12a01743e8640674f8d6d
Reviewed-on: https://code-review.googlesource.com/c/gocloud/+/57151
Reviewed-by: Cody Oss <codyoss@google.com>
diff --git a/spanner/integration_test.go b/spanner/integration_test.go
index aa0ee91..1770ab0 100644
--- a/spanner/integration_test.go
+++ b/spanner/integration_test.go
@@ -2691,6 +2691,8 @@
 }
 
 func TestIntegration_StartBackupOperation(t *testing.T) {
+	t.Skip("https://github.com/googleapis/google-cloud-go/issues/2393")
+
 	skipEmulatorTest(t)
 	t.Parallel()