this derivation will be built:
  /nix/store/38gzdkdxgf2fp7abdpf40cryfaw2if9m-interpolate-conformance.drv
bld4: building 38gzdkdxgf2fp7abdpf40cryfaw2if9m-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected