this derivation will be built:
  /nix/store/ciiax6xv1hs3s2jqwj5vbc8l7vvxnlis-interpolate-conformance.drv
bld4: building ciiax6xv1hs3s2jqwj5vbc8l7vvxnlis-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected