Investigate GitHub App large-scale repository syncing

Created by: pjlast

Currently GitHub App repository syncing starts failing for large repository lists

See here: https://sourcegraph.slack.com/archives/CMBA8F926/p1661163744887069

And here: https://sourcegraph.slack.com/archives/C02EDAQAJQZ/p1661165381091019

I suspect it has something to do with the access token being refreshed, but this needs to be investigated.