Fixed schema test for Oracle 11.2.0.1 which is used in Django Project's CI.

Refs #23073 Workaround.

Refs #22738 Repeats the mysql "offense". When the issue is solved, the
Oracle special case should be made to play with the solution (that is,
Oracle should be fixed the same way that mysql and the 3rd-party backneds
are).
Update squashmigration docs to also mention circ dep errs (refs #23337)
Added docstring forgotten in 56252e7.