Fix this mypy typcheck error in the test builder:
testScriptWithTypes:52: error: Argument 1 to "wait_until_tty_matches" of
"Machine" has incompatible type "int"; expected "str"
system1.wait_until_tty_matches(2, "login: ")
This makes the test succeed again.
flake.lock previously included a "indirect" reference to nixpkgs.
I am not sure what this means but I added `inputs.nixpkgs` and updated nixpkgs because this old version of nixpkgs didn't have any support for aarch64-darwin at all.
Now on a aarch64-darwin I can type `nix build` and get a working version of agenix.
