Installation fails if `python` is not installed on host system

[Baltoli]

On macOS 12.3 Monterey (at least, I've not verified other versions), there is no python installed. This causes the action to fail with the following error:

> Run cachix/install-nix-action@v17
The node12 is not supported on macOS ARM6[4](https://github.com/runtimeverification/llvm-backend/runs/7196589297?check_suite_focus=true#step:3:5) platform. Use node16 instead.
/Users/user/actions-runner/_work/_actions/cachix/install-nix-action/v17/lib/install-nix.sh: line 41: python: command not found
node:child_process:867
    throw err;
    ^
Error: Command failed: /Users/user/actions-runner/_work/_actions/cachix/install-nix-action/v17/lib/install-nix.sh
(...etc)

Would it be possible to add an option to use python3 at this point in the installation script?

[domenkozar]

That's a shame. Is there python3?

[Baltoli]

Yes, python3 is available.

[silviogutierrez]

It's actually not available on Ubuntu either, at least 20.04 onwards. So self-hosted runners will fail unless they have python installed. See:

https://itsfoss.com/python-not-found-ubuntu/

So the best bet is to document that python needs to be available in the runner or maybe try python3 which should cover most situations.