this derivation will be built:
  /nix/store/5cd79az7sj6q6rbry99m0nwd005dh5qg-interpolate-conformance.drv
bld4: building 5cd79az7sj6q6rbry99m0nwd005dh5qg-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected