Ready tests for ChainIndex

[idky137]

Prepare tests for chain index integration.

Motivation

Several changes to tests are required for chain index integration, these changes should be made first so we know any failure introduced in the switchover are from the chain index code and not from test changes.

Solution

• Update default regtest activation heights and fix tests for changes.
• Add #[tokio::test(flavor = "multi_thread", worker_threads = 2)] to tests that will require it after update.

Tests

Updates tests in place

Specifications & References

Follow-up Work

• Chain index integration #596

PR Checklist

• The PR name is suitable for the release notes.
• The solution is tested.
• The documentation is up to date.