this derivation will be built:
  /nix/store/53dd7nxps2z30fszkrpqwl04ylxlz25r-interpolate-conformance.drv
bld4: building 53dd7nxps2z30fszkrpqwl04ylxlz25r-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected