Improve runner deletion by using busy flag

[gertjanmaas]

When building this solution the Github API couldn't tell if a runner was busy or not, so we resorted to trying to delete each runner via de API. If that returned a 500 Internal Server Error, we would know if it was busy.

Just played with the API again and saw the busy flag was added for runners. See https://docs.github.com/en/rest/reference/actions#list-self-hosted-runners-for-a-repository

Instead of trying to delete a runner we should use this flag so reduce the number of API calls on Github.

[samuelb]

The admin of the Github Enterprise installation we have in our company came to me and complained that 99% of the HTTP 500 errors are coming from our Github Actions runners. While I understand that this is technically not a problem, I fear that every time there is an issue with Github Enterprise, they will find those HTTP 500s in the logs and I have to explain the situation to them. So I would appreciate if those HTTP 500 would be gone or get reduced :)

[ScottGuymer]

Looking at the code this behaviour is in the scale-down lambda somewhere here

Do you think you would be able to create a PR to enhance this? Would be more than happy to review.

[samuelb]

I already tried to change it by my own. Since I never worked with TypeScript before, I'm struggling with the unit tests at least. With what I ended up two days ago can be found in this branch.

[ulich]

@samuelb I'm happy to assist and continue the work from you and create a PR. Would you be ok with that?