this derivation will be built:
  /nix/store/dbzy4s13j5xvcr2vdw3sqdlj6abik213-interpolate-conformance.drv
bld4: building dbzy4s13j5xvcr2vdw3sqdlj6abik213-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected