docs: fix javadoc code example for awaitOptimizeRestoredTableAsync (#1617)

Fixes rendering of https://cloud.google.com/java/docs/reference/google-cloud-bigtable/latest/com.google.cloud.bigtable.admin.v2.BigtableTableAdminClient#com_google_cloud_bigtable_admin_v2_BigtableTableAdminClient_awaitOptimizeRestoredTableAsync_com_google_cloud_bigtable_admin_v2_models_OptimizeRestoredTableOperationToken_

Author: kolea2

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/admin/v2/BigtableTableAdminClient.java

@@ -1218,7 +1218,8 @@ public void awaitOptimizeRestoredTable(OptimizeRestoredTableOperationToken token
  awaitOptimizeRestoredTableAsync(token).get();
  }
 
- /** Awaits a restored table is fully optimized asynchronously.
+ /**
+ * Awaits a restored table is fully optimized asynchronously.
  *
  * <p>Sample code
  *
@@ -1241,7 +1242,8 @@ public void awaitOptimizeRestoredTable(OptimizeRestoredTableOperationToken token
  * },
  * MoreExecutors.directExecutor()
  * );
- * */
+ * }</pre>
+ */
  public ApiFuture<Void> awaitOptimizeRestoredTableAsync(
  OptimizeRestoredTableOperationToken token) {
  return transformToVoid(