this derivation will be built:
  /nix/store/49rcy7xz943kj5s3z8ijv0w5519sjhdq-interpolate-conformance.drv
bld4: building 49rcy7xz943kj5s3z8ijv0w5519sjhdq-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected