ci: re-enable test migrations in release workflow

[johnstcn]

Tested here: https://github.com/coder/coder/actions/runs/9126619620/job/25095263706#step:17:101

Also makes the output "friendlier" in case of failure:

Migrating from version "9f4d2966a" to "f23d4802b" failed:
        migrate setup: create iofs: failed to init driver with path .: duplicate migration file: 000208_notification_banners.down.sql
Check the following:
 - All migrations from version "f23d4802b" must exist in version "9f4d2966a" with the same migration numbers.
 - Each migration must have the same effect.
 - There must be no gaps or duplicates in the migration numbers.