Fix RocksDBException: Busy during snapsync

[siladu]

PR description

Make TrieNodeHealingRequest.requiresPersisting thread safe.

Fixed Issue(s)

Fixes #7619

Testing

This is a hard to trigger race condition. Before this PR, the number of occurrences of this error was ~1 / 20 syncing nodes.
This has been tested on 60 nodes with CHECKPOINT sync and 20 nodes with SNAP sync and found no issues up to and including flat db healing. A few suffered from Backward sync halts but that is a later phase in the sync so I think unrelated.

Thanks for sending a pull request! Have you done the following?

• Checked out our contribution guidelines?
• Considered documentation and added the doc-change-required label to this PR if updates are required.
• Considered the changelog and included an update if required.
• For database changes (e.g. KeyValueSegmentIdentifier) considered compatibility and performed forwards and backwards compatibility tests

Locally, you can run these tests to catch failures early:

• unit tests: ./gradlew build
• acceptance tests: ./gradlew acceptanceTest
• integration tests: ./gradlew integrationTest
• reference tests: ./gradlew ethereum:referenceTests:referenceTests

[siladu]

Had to open #7746 to add changelog