Go migrations run even if they are outside of the target migrations directory

[rafalneves]

For our specific migration process, we need a way to distinguish between different types of migrations. This means running goose as many times as different kinds of migrations we have, once for each. This should happen on the same binary. We decided to split different types of migrations into different folders and just call goose for each one of them, and all went well, till we started to create Go migrations.

All pending Go migrations are executed in the first run goose, as they are loaded regardless of being in the target fs folder:

	// Go migrations registered via goose.AddMigration().
	for _, migration := range registeredGoMigrations {
		v, err := NumericComponent(migration.Source)
		if err != nil {
			return nil, err
		}
		if versionFilter(v, current, target) {
			migrations = append(migrations, migration)
		}
	}

We should check if the migration belongs to the target file list before loading it up.