Don't load test env by default
HashWithIndifferentAccess better respects #to_hash

In particular, `.new`, `#update`, `#merge`, `#replace` all accept
objects which respond to `#to_hash`, even if those objects are not
Hashes directly.
PostgreSQL, use `PostgreSQLColumn` in PG specific tests.
Merge pull request #12778 from etehtsea/rake-default-fix

Don't load test env by default.

Closes #13241
Add CHANGELOG entry for #12778 [ci skip]
Merge pull request #12550 from Peeja/hash-wia-update-respects-to-hash

HashWithIndifferentAccess#update respects #to_hash
Refactor test to use DdlHelper.

Follow-Up to https://github.com/rails/rails/pull/14400

This ensures that all tables are removed after each test and thereby
allowing us to run the tests in a random order.