this derivation will be built:
  /nix/store/g3cs6880k0mcq14r2vwmfyhr1g7x40mb-interpolate-conformance.drv
bld4: building g3cs6880k0mcq14r2vwmfyhr1g7x40mb-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected