[Bug] Flink bounded source with checkpoint missing last snapshot commit

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/paimon/issues) and found nothing similar.

### Paimon version

Paimon 0.9 snapshot

### Compute Engine

Flink

### Minimal reproduce step

If use flink bounded source which like jdbc or other, with checkpoint enabled,flink do not commit last snapshot commit.
I review the source code find org.apache.paimon.flink.sink.CommitterOperator caused it.
I do not know why their should skip commit snapshot if flink streaming mode enable checkpoint.

### What doesn't meet your expectations?

Missing last commit

### Anything else?

_No response_

### Are you willing to submit a PR?

- [X] I'm willing to submit a PR!

Start with org.apache.paimon.flink.sink.CommitterOperator and the reported bounded-source reproduction using checkpointing. Trace why the final snapshot commit is skipped when Flink streaming mode is enabled. Done means the last snapshot is committed for a bounded source, with the behavior verified against the reproduction.

Written by the indexing model from the issue text.