Test all database migrations from db-version/42 onwards

While a bit arbitrary choosing 42, it is from more than two years ago. We can use this as our new baseline, in that this test will always check upgrades from 42 onwards, with each database bump.

Once the test was up and running, it immediately identified a bug in the database migration for v50 and v57. These have been fixed in this branch too.

Fixes #778 (closed).

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