Make clean_slot_dict function also delete ci_test trigger info

MRs !316 (merged) and !317 (merged) added a trigger field to the slot['metadata']['ci_test'] field to implement LHCbPR2HD!180 (merged).

I'm not 100% sure but I think these fields should be added to the clean_slot_dict function such that a comparison of slots ignores these.
This would only restore the same behavior as before the MRs above.
I wonder if it might even make sense to just delete the ['ci_test'] field? But I don't think I grasp enough of the surrounding infrastructure.

Hoping @clemenci could have a look and tell me if this is ok? Thanks! 🙏

cc @maszyman