Fixes #17621. This 5 year old (or older) issue causes validations to fire
when a parent record has `validate: false` option and a child record is
saved. It's not the responsibility of the model to validate an
associated object unless the object was created or modified by the
parent.

Clean up tests related to validations

`assert_nothing_raised` is not benefiting us in these tests
Corrected spelling of "respects"
It's better to use `assert_not_operator` over `assert !r.valid`