Failed test test_multiple_find_or_create_by_within_transactions

Tests:
- CreateOrFindByWithinTransactions#test_multiple_find_or_create_by_bang_within_transactions
- CreateOrFindByWithinTransactions#test_multiple_find_or_create_by_within_transactions

The second thread is running both `ROLLBACK` and `COMMIT` at some point, hence the unwanted error: _no transaction in progress_.

The bug appears at the end of the transaction block ([source](https://github.com/rails/rails/blob/7130e3cfc4a09d76df6e86531bbd6bb95bc081e6/activerecord/test/cases/relations_test.rb#L2495)).

Start with the two named CreateOrFindByWithinTransactions tests and inspect the transaction block in activerecord/test/cases/relations_test.rb at the linked location. Reproduce the concurrent failure and trace the second thread's ROLLBACK and COMMIT calls; done means both tests pass without the “no transaction in progress” error.

Written by the indexing model from the issue text.