this derivation will be built:
  /nix/store/m1mlq4zz9a9v0k1sc52xxhfzyn8g9dqn-interpolate-conformance.drv
bld4: building m1mlq4zz9a9v0k1sc52xxhfzyn8g9dqn-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected