force push breaks github integration

[lukemarsden]

seemingly if you force push a repo (e.g. to a previous commit), github integration doesn't update the commit in the app

[lukemarsden]

api-1  | 2024-07-17T11:02:29Z ERR pkg/server/github_handlers.go:131 > error updating github app: failed to pull repo: non-fast-forward update

[lukemarsden]

we shouldn't be pulling, we should be fetching and then checking out the specific commit included in the github webhook (and then, we also need to be dealing with different branches)

[lukemarsden]

per pkg/github/utils.go