Intermittent "No valid build found in GUS" error for valid build

In https://github.com/heroku/heroku-buildpack-python/issues/1012 after adding the label, Git2Gus commented with:

> Error while creating work item. No valid build foundin GUS!

The build specified in `.git2gus/config.json` was valid. Labels had been added to multiple GitHub issues at once (3-4 issues), and the others were added successfully the first time. Removing and re-adding the label to the linked issue cause the work item to be created successfully.

I believe the GUS API call to resolve the build must have failed for a different reason, but the handling here doesn't take that into account:
https://github.com/forcedotcom/git2gus/blob/dbe8c53c7bf703d7607ca595ef0a473a843eb3b9/api/services/Gus/resolveBuild.js
https://github.com/forcedotcom/git2gus/blob/f992e387902f344be7ba359d595c6fdcbaa9b4c9/api/actions/createWorkItem.js#L107-L109

There's also a typo in the error message, "foundin" should be "found in".

Ideally Git2Gus would also retry after a failure, to save having to remove and re-add the label.