`wait_container_is_ready` throwing TimeoutException on first try

After updating to v3.5.0 our tests using `PostgresContainer`s are failing.

My guess is that this has to do with the changes regarding transient exceptions. We use `psycopg2` and the error thrown on unsuccessful connection is not inheriting `sqlalchemy.exc.OperationalError` but rather is a plain `AttributeError` with message:

```'NoneType' object has no attribute '_stan_scope'```