replace `protobot/stale` with `actions/stale`

[thesuperzapper]

It seems like there are issues with the GitHub protobot/stale application probot/stale#385, probot/stale#384, probot/stale#378, and given that the protobot seems to have been abandoned, the main alternative is now to use actions/stale in a GitHub actions workflow.

PS: the stale bot becoming abandoned is almost too much irony for me to handle.

[stale]

This issue has been automatically marked as stale because it has not had activity in 60 days.
It will be closed in 7 days if no further activity occurs.

Thank you for your contributions.

---

Issues never become stale if any of the following is true:

1. they are added to a Project
2. they are added to a Milestone
3. they have the lifecycle/frozen label

[thesuperzapper]

Well, isn't this ironic?