Fix SQLite tests

[woylie]

Thanks to @martosaur, we can run tests on SQLite with mix test.sqlite now. A bunch of tests are failing. We can track the progress in this issue.

• ilike: Not supported by SQLite.
• like tests: Is case-insensitive in SQLite, which causes tests to fail.
• offset requires limit in SQLite. For unlimited result set, use limit -1.
• empty/not_empty operators
• character escape in like queries: Flop escapes %, _, and \\ in filter strings for like/ilike operators. SQLite requires to specify escape characters with ESCAPE (see https://www.sqlitetutor.com/escape/).
• tests with postgres composite types can be skipped

After fixing everything

• run mix test.all in tests job of GH actions workflow
• change mix coveralls.json.all to run tests on all adapters