Fix DDL non-conditionality re SQL Server

[RudolfCardinal]

No description provided.

[RudolfCardinal]

One test requires Python 3.10+ to run (because it uses unittest.TestCase.assertNoLogs). But it runs successfully on Python 3.10. Below that version, it will warn but pass.

[martinburchell]

Looks good to me and tested OK with CamCOPS, at least with MySQL.

There's some Python < 3.10 workarounds for assertNoLogs() discussed at https://stackoverflow.com/questions/35871815/python-3-unit-testing-assert-logger-not-called and I think we can live without the test for Python 3.9. I'm also wary of tests that assert nothing happens but in this case we do have the "something happens" test alongside it so if someone removed the message at least one of the tests would break.