buildchecker: do not fail when checking org membership
Created by: bobheadxi
Buildchecker is currently stuck on this API call: https://github.com/sourcegraph/sourcegraph/runs/7885574019?check_suite_focus=true#step:4:54
It seems we get a 404 which is strange, instead of just a nil membership like before - maybe new behaviour from GitHub?
Test plan
recorded tests continue to pass