Fix race condition in TestRunMigratorMigrationChangesDirection

Created by: mrnugget

We've talked about this before (and I already took a stab at it but it went nowhere), so let's create a ticket for this since it failed again here:

FAIL: TestRunMigratorMigrationChangesDirection (0.00s) | 0s
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  | runner_test.go:248: unexpected number of calls to Up. want=5 have=4