Purpose of this pull request

This PR fix CheckpointCoordinator report NPE when ack not existed pending checkpoint. Ack the not existed pending checkpoint could be found when TaskAcknowledgeOperation execute more than once. This PR is considered a system robustness fix.

Does this PR introduce any user-facing change?

no

How was this patch tested?

add new test

Check list

• If any new Jar binary package adding in your PR, please add License Notice according
  New License Guide
• If necessary, please update the documentation to describe the new feature. https://github.com/apache/seatunnel/tree/dev/docs
• If you are contributing the connector code, please check that the following files are updated:
  1. Update change log that in connector document. For more details you can refer to connector-v2
  2. Update plugin-mapping.properties and add new connector information in it
  3. Update the pom file of seatunnel-dist
• Update the release-note.