Make sure send_unknown_user_type_stats is never run in quick succession
Make sure send_unknown_user_type_stats is never run in quick succession

Because quickcache doesn't use request coalescing, this will only block
rerunning it after a run has finished, but that's good enough protection
for us at this point.

dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq