this derivation will be built:
  /nix/store/74zh0ikag1cfgp4warx6nhvmiyr8hcx8-interpolate-conformance.drv
bld4: building 74zh0ikag1cfgp4warx6nhvmiyr8hcx8-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected