## What changed?
<!-- Describe what has changed in this PR -->
- Drop unknown fields when replicating workflow state
## Why?
<!-- Tell your future self why have you made these changes -->
- This is to prevent a newly introduced, cell specific field got
accidentally replicated to the target cluster after source cluster
rolling back.
## How did you test it?
<!-- How have you verified this change? Tested locally? Added a unit
test? Checked in staging env? -->
- Unit test
## Potential risks
<!-- Assuming the worst case, what can be broken when deploying this
change to production? -->
## Documentation
<!-- Have you made sure this change doesn't falsify anything currently
stated in `docs/`? If significant
new behavior is added, have you described that in `docs/`? -->
## Is hotfix candidate?
<!-- Is this PR a hotfix candidate or does it require a notification to
be sent to the broader community? (Yes/No) -->
