this derivation will be built:
  /nix/store/nb59yx515c9rxfqjmqy5lfn5p20ziglz-interpolate-conformance.drv
bld4: building nb59yx515c9rxfqjmqy5lfn5p20ziglz-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected