GC is too aggressive for user integrations

1. Schedule integration for qt5
2. Cancel integration before it has finished (has successful workitems)
3. Reschedule integration
4. Cancel integration
5. Execute manual gc

Expectation:

 All workitems should be conserved because last failed and cancelled qt5 integrations that were built after the 1st successful integration should be protected. That condition is valid in this case.

Result:

 All workitems are cleaned by the gc.