fix: Make change stream unknown mod error more actionable (#1938)

* fix: Make change stream unknown mod error more actionable * 🦉 Updates from OwlBot post-processor See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md --------- Co-authored-by: Igor Bernstein <igorbernstein@google.com> Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: 3 people

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/stub/changestream/ChangeStreamStateMachine.java

@@ -486,7 +486,8 @@ State handleDataChange(ReadChangeStreamResponse.DataChange dataChange) {
  Value.fromProto(mod.getAddToCell().getTimestamp()),
  Value.fromProto(mod.getAddToCell().getInput()));
  }
- throw new IllegalStateException("AWAITING_NEW_DATA_CHANGE: Unexpected mod type");
+ throw new IllegalStateException(
+ "Received unknown mod type. You may need to upgrade your Bigtable client.");
  }
 
  // After adding all mods from this DataChange to the state machine, finish the current