Log Message:
databases/py-peewee: Update to 3.3.0. Clean up.

- Added support for SQLite's new ON CONFLICT clause, which is modelled
  on the syntax used by Postgresql and will be available in SQLite
  3.24.0 and onward.
- Added better support for using common table expressions and a
  cleaner way of implementing recursive CTEs, both of which are also
  tested with integration tests (as opposed to just checking the
  generated SQL).
- Modernized the CI environment to utilize the latest MariaDB
  features, so we can test window functions and CTEs with MySQL (when
  available).
- Reorganized and unified the feature-flags in the test suite.