this derivation will be built:
  /nix/store/m3fmz0ylqx1alnsc60qyixqwszpvwmy4-interpolate-conformance.drv
bld4: building m3fmz0ylqx1alnsc60qyixqwszpvwmy4-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected