Try to repair oddball test bots timing out in test_int (#119166)

Try to repair oddball test bots timing out in test_int (#119166)

Various test bots (outside the ones GH normally runs) are timing out during test_int after ecd8664 (asymptotically faster str->int). Best guess is that they don't build the C _decimal module. So require that module in the most likely tests to time out then. Flying mostly blind, though!