[fix][txn] Fix SnapshotSegmentAbortedTxnProcessorImpl thread safety issue

[nikam14]

Fixes #22116

Motivation

Fix SnapshotSegmentAbortedTxnProcessorImpl thread safety issue

Modifications

1. Added volatile keyword to unsealedtxnIds variable.
2. Same resource were accessed at same line , so modified it.
3. Added synchronized keyword for data consistency

Verifying this change

• [x] Make sure that the change passes the CI checks.

Documentation

• [ ] doc
• [ ] doc-required
• [x] doc-not-needed
• [ ] doc-complete

Matching PR in forked repository

PR in forked repository:

[nikam14]

Thanks for the explanation @lhotari