this derivation will be built:
  /nix/store/ah7f087y7x1ij5250blpkc4v7msxmnwp-interpolate-conformance.drv
bld4: building ah7f087y7x1ij5250blpkc4v7msxmnwp-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected