delete_where() fails to commit in 3.x

[simonw]

We fixed this in 4.0 but it's actually a bug in 3.x that I think deserves a dot-release fix.

[simonw]

This means users who are not yet ready to upgrade to sqlite-utils 4 will be able to fix this bug by pinning to sqlite-utils>=3.39.1.

[simonw]

That commit failed due to Black, so I disabled Black in test.yml for the 3.x branch because I don't want to upgrade to latest formatting just for this one bug fix.