Make `submissions_canceled` and `add_chunks_done_to_submissions_failed` migrations bidirectional

Most of the migrations have both a `.up.sql` and a `.down.sql`.

However, it seems like we missed this in three recent PRs
- https://github.com/channable/opsqueue/pull/75
- https://github.com/channable/opsqueue/pull/108
- https://github.com/channable/opsqueue/pull/123

Making those migrations reversible is only a couple of minutes of work, so I think it would be good to do so.

- Check this in CI so the wrong command is no longer used.

Find the migrations named submissions_canceled and add_chunks_done_to_submissions_failed, then compare their .up.sql and .down.sql files with neighboring reversible migrations. Check the existing CI migration command, add the missing reverse migrations, and verify CI rejects migrations that are not bidirectional.

Scritto dal modello di indicizzazione a partire dal testo della issue.