[hooks] fix timestamp confusion in TransactionsCleanupStartupHook transactions.tx_time is inserted as datetime.utcnow(), in server/sources/native.py:NativeSQLSource.start_undoable_transaction. Don't compare it to datetime.now().

from os.path import join
assert __file__.endswith(join('scripts', 'script3.py')), __file__
assert '__main__' == __name__, __name__
assert ['-vd', '-f', 'FILE.TXT'] == __args__, __args__