datastore: Fix storage cleanup's handling of timezones

Timestamps in the `storage_cleanups` table are stored without timezones,
but our timezone handling in `AcquireNextStorage()` is inconsistent: we
typically just use `NOW()` to get the current timestamp, but in one case
we use `NOW() AT TIME ZONE 'UTC'`. In some setups, this leads to time
stamps which cannot be correctly compared with each other.

Fix the bug by consistently storing time stamps without time zones. This
bug is similar to 4a2ac0ed (datastore: Fix acknowledgement of stale
jobs considering timezones, 2021-08-20).

Changelog: fixed

internal/praefect/datastore/storage_cleanup.go

@@ -71,7 +71,7 @@ func (ss *StorageCleanup) AcquireNextStorage(ctx context.Context, inactive, upda
 	if err := ss.db.QueryRowContext(
 		ctx,
 		`UPDATE storage_cleanups
-			SET triggered_at = (NOW() AT TIME ZONE 'UTC')
+			SET triggered_at = NOW()
 			WHERE (virtual_storage, storage) IN (
 				SELECT virtual_storage, storage
 				FROM storage_cleanups