Confusing message when attempting downgrade of database schema

[p12tic]

Buildbot does not support downgrade of database schema. However, when attempting to do so Buildbot throws a confusing error (taken from #7396 (comment)):

db-1        | ERROR:  relation "version" does not exist at character 15
db-1        | STATEMENT:  select * from version limit 1
db-1        | ERROR:  relation "migrate_version" does not exist at character 15
db-1        | STATEMENT:  select * from migrate_version limit 1
buildbot-1  | Got fatal Exception on DB
buildbot-1  | Traceback (most recent call last):
buildbot-1  |   File "/buildbot_venv/lib/python3.9/site-packages/twisted/python/threadpool.py", line 285, in <lambda>
buildbot-1  |     inContext.theWork = lambda: context.call(  # type: ignore[attr-defined]
buildbot-1  |   File "/buildbot_venv/lib/python3.9/site-packages/twisted/python/context.py", line 117, in callWithContext
buildbot-1  |     return self.currentContext().callWithContext(ctx, func, *args, **kw)
buildbot-1  |   File "/buildbot_venv/lib/python3.9/site-packages/twisted/python/context.py", line 82, in callWithContext
buildbot-1  |     return func(*args, **kw)
buildbot-1  |   File "/buildbot_venv/lib/python3.9/site-packages/buildbot/db/pool.py", line 234, in __thd
buildbot-1  |     log.err(e, 'Got fatal Exception on DB')
buildbot-1  | --- <exception caught here> ---
buildbot-1  |   File "/buildbot_venv/lib/python3.9/site-packages/buildbot/db/pool.py", line 207, in __thd
buildbot-1  |     rv = callable(arg, *args, **kwargs)
buildbot-1  |   File "/buildbot_venv/lib/python3.9/site-packages/buildbot/db/model.py", line 1136, in thd
buildbot-1  |     context.run_migrations()
buildbot-1  |   File "/buildbot_venv/lib/python3.9/site-packages/alembic/runtime/migration.py", line 615, in run_migrations
buildbot-1  |     for step in self._migrations_fn(heads, self):
buildbot-1  |   File "/buildbot_venv/lib/python3.9/site-packages/buildbot/db/model.py", line 1122, in upgrade
buildbot-1  |     return alembic_scripts._upgrade_revs(current_script_rev_head, rev)
buildbot-1  |   File "/buildbot_venv/lib/python3.9/site-packages/alembic/script/base.py", line 455, in _upgrade_revs
buildbot-1  |     return [
buildbot-1  |   File "/usr/lib/python3.9/contextlib.py", line 135, in __exit__
buildbot-1  |     self.gen.throw(type, value, traceback)
buildbot-1  |   File "/buildbot_venv/lib/python3.9/site-packages/alembic/script/base.py", line 283, in _catch_revision_errors
buildbot-1  |     raise util.CommandError(resolution) from re
buildbot-1  | alembic.util.exc.CommandError: Can't locate revision identified by '066'

Buildbot should show a proper error message and refuse to do anything.