Registers a default runner with ubuntu OS or executes user's OCI container with podman.
## Nix runner
We provide a `runs-on: nix` runner which executes nix commands in a nix user environment on the build server.
Uses previously built derivations, which speeds up builds. Note that user-configured substitutors do not work (this is currently nix limitation of nix.)
⚠️ Builds use the system's nix-store in a unpriviledged mode, so derivations may be seen and used by other builds by this runner.
Consequentially, don't use to build nix things that should stay secret (which is a bad idea anyway).
To create a new token for registration, follow the steps outlined in the [Forgejo documentation](https://forgejo.org/docs/latest/user/actions/#forgejo-runner).
