this derivation will be built:
  /nix/store/r1gfzm8lf8y63my72s418cqwd6ns7aj2-interpolate-conformance.drv
bld4: building r1gfzm8lf8y63my72s418cqwd6ns7aj2-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected