fix: Add UNKNOWN to retry code, the same set was used for request level retries. (#3034)

* Update WriteToDefaultStream.java * add unknown to retry code * remove unwanted change.

Author: yirutang

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

@@ -1254,7 +1254,8 @@ private boolean isConnectionErrorRetriable(Code statusCode) {
  || statusCode == Code.UNAVAILABLE
  || statusCode == Code.CANCELLED
  || statusCode == Code.INTERNAL
- || statusCode == Code.DEADLINE_EXCEEDED;
+ || statusCode == Code.DEADLINE_EXCEEDED
+ || statusCode == Code.UNKNOWN;
  }
 
  private boolean useBackoffForError(Code statusCode, String streamName) {