GitHub runners not being reused or cleaned up

[Gussy]

What happened?

Every time tartlet creates new VMs it fails to register the runner if the runner with that name already exists. The only way to get the runner to register is to delete the old runners from github.

This is with a personal github account and repo runners.

What are the steps to reproduce?

1. Start tartlet
2. VMs start up and github runners appear in https://github.com/<user>/<repo>/settings/actions/runners
3. Restart tartlet (or the host running it)
4. VMs start and the github runner install can be seen to fail in the terminal due to that runner already existing

What is the expected behavior?

Tartlet should either re-use the runners it has already added to that repo, or cleanup old runners before adding new ones.