fix: Add back the accidentally removed background executor provider

google-cloud-bigquerystorage/src/main/java/com/google/cloud/bigquery/storage/v1/StreamWriter.java

@@ -279,6 +279,7 @@ private BigQueryWriteClient getBigQueryWriteClient(Builder builder) throws IOExc
           BigQueryWriteSettings.newBuilder()
               .setCredentialsProvider(builder.credentialsProvider)
               .setTransportChannelProvider(builder.channelProvider)
+              .setBackgroundExecutorProvider(builder.executorProvider)
               .setEndpoint(builder.endpoint)
               .build();
       testOnlyClientCreatedTimes++;