bug: GitHub status check does not wait for builds to start

[BYK]

Sometimes, when Craft is faster than GitHub and status check integrations, Craft cannot find any relevant checks, even in pending state and immediately fails: https://github.com/getsentry/onpremise/runs/777959403?check_suite_focus=true

We should figure out a way to address this issue either by trying a few times when there are no checks listed or trying to find actual integrations and match that number with the checks reported.

[BYK]

Looks like we can use the check suites API to get a list of pending suites even if the check runs never start/report in.

We should only fail with a NOT_FOUND when all the pending suites are completed and we still cannot find the context.

Sample response for a check suites call with 0 check runs: https://gist.github.com/BYK/dad1a1b32dcec60201be5d0efc8eff08

[chadwhitacre]

Apparently #117 did not fully resolve the issue.