ci(migration-sql): checkout base commit to figure out the base revision

[sid-maddy]

This avoids having to reimplement Alembic's revision graph logic.

[github-actions]

alembic upgrade --sql $base:head

INFO  [alembic.runtime.migration] Context impl PostgresqlImpl.
INFO  [alembic.runtime.migration] Generating static SQL
INFO  [alembic.runtime.migration] Will assume transactional DDL.
INFO  [alembic.runtime.migration] Running upgrade 6991bcb18f89 -> ca14e3688152, Make datetimes timezone-aware

BEGIN;

-- Running upgrade 6991bcb18f89 -> ca14e3688152

ALTER TABLE scans ALTER COLUMN queued_at TYPE TIMESTAMP WITH TIME ZONE;

ALTER TABLE scans ALTER COLUMN pending_at TYPE TIMESTAMP WITH TIME ZONE;

ALTER TABLE scans ALTER COLUMN finished_at TYPE TIMESTAMP WITH TIME ZONE;

ALTER TABLE scans ALTER COLUMN reported_at TYPE TIMESTAMP WITH TIME ZONE;

UPDATE alembic_version SET version_num='ca14e3688152' WHERE alembic_version.version_num = '6991bcb18f89';

COMMIT;

alembic downgrade --sql head:$base

INFO  [alembic.runtime.migration] Context impl PostgresqlImpl.
INFO  [alembic.runtime.migration] Generating static SQL
INFO  [alembic.runtime.migration] Will assume transactional DDL.
INFO  [alembic.runtime.migration] Running downgrade ca14e3688152 -> 6991bcb18f89, Make datetimes timezone-aware

BEGIN;

-- Running downgrade ca14e3688152 -> 6991bcb18f89

ALTER TABLE scans ALTER COLUMN reported_at TYPE TIMESTAMP WITHOUT TIME ZONE;

ALTER TABLE scans ALTER COLUMN finished_at TYPE TIMESTAMP WITHOUT TIME ZONE;

ALTER TABLE scans ALTER COLUMN pending_at TYPE TIMESTAMP WITHOUT TIME ZONE;

ALTER TABLE scans ALTER COLUMN queued_at TYPE TIMESTAMP WITHOUT TIME ZONE;

UPDATE alembic_version SET version_num='6991bcb18f89' WHERE alembic_version.version_num = 'ca14e3688152';

COMMIT;