x/build/cmd/gopherbot, x/build/maintner: "close stale WaitingForInfo" task failing on non-existing issue

[dmitshur]

From gopherbot logs:

2020/07/10 13:33:30 close stale WaitingForInfo: POST https://api.github.com/repos/golang/go/issues/39453/comments: 422 Validation Failed [{Resource:IssueComment Field:data Code:unprocessable Message:Could not resolve to a node with the global id of 'MDU6SXNzdWU2MzM4NzY4NTM='.}]
2020/07/10 13:33:30 gopherbot ran in 9.88987365s

Issue #39453 is 404. gopherbot should handle this situation as a non-error. Treating it as an error adds an unnecessary sleep:

2020/07/10 13:33:30 sleeping 30s after previous error.

It's possible this is a bug or unexpected behavior on the GitHub API side (might be worth reporting it to them), but if it persists, we should just update gopherbot to handle it.

It's also worth investigating if this is an issue that can and is better to fix in maintner, rather than gopherbot.

/cc @golang/osp-team