fix test issue

Author: sakthivelmanii

samples/snippets/src/test/java/com/example/spanner/SpannerSampleIT.java

@@ -43,6 +43,7 @@
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.PrintStream;
+import java.time.Duration;
 import java.util.UUID;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Predicate;
@@ -590,6 +591,7 @@ public void testEncryptedDatabaseAndBackupSamples() throws Exception {
     } finally {
       // Delete the backups from the test instance first, as the instance can only be deleted once
       // all backups have been deleted.
+      Uninterruptibles.sleepUninterruptibly(60, TimeUnit.SECONDS);
       System.out.println("Deleting backups ...");
       deleteAllBackups(instanceId);
       instanceAdminClient.deleteInstance(instanceId);