- Don't use `printf` for the expected result, but just use bash's `$' '`
  litteral strings
- Quote the `nix` call result
- Invert the order in the comparisons (just because it feels more
  natural)

Also add a disabled test for when the `--override-input` flag comes
*before* the flake ref

`--override-input` id snarky because it takes two arguments, so it
doesn't play well when completed in the middle of the CLI (since the
argument just after gets interpreted as its second argument). So use
`--update-input` instead

- Test another command than `build`
- Test with two input flakes