this derivation will be built:
  /nix/store/daqwz7qzkyl9ryk62inc9jyjr2w9m8m6-interpolate-conformance.drv
bld4: building daqwz7qzkyl9ryk62inc9jyjr2w9m8m6-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected