Remove Flaky Test Workarounds

[metaskills]

If we are happy that things are more green with the foreign key check but, I'd like to see if we can:

• Remove the undefined coercion of all ConcurrentTransactionTest cases.
• Move to 1 vs 3 ActiveRecord test case batches in bin/_test file.
• Maybe move more tests together?

[metaskills]

Following up from this Flaky Tests & Foreign Key Checks section, I just noticed that the retry stuff is working. Likely the sleeps help it a bit while Aurora gets its FK bearings. Here are some notes I kept when recording some HABTM test failure counts. Not shown here was the preceding test prior to the failure where I wanted to make sure there was not a toxic test in the stack elsewhere. A pattern never showed up.

• HasAndBelongsToManyAssociationsTest (8) test_adding_single (5) test_adding_from_the_project (4) test_adding_from_the_project_fixed_timestamp (6) test_has_and_belongs_to_many (6) test_count (2) test_find_in_association_with_options (2) test_habtm_distinct_order_preserved