this derivation will be built:
  /nix/store/rpm70s7ss0lfffxylad1fqy9zxvvck2d-interpolate-conformance.drv
bld4: building rpm70s7ss0lfffxylad1fqy9zxvvck2d-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected