this derivation will be built:
  /nix/store/9vckdjl68bcjrqknfv2zkhjczm744q9z-interpolate-conformance.drv
bld4: building 9vckdjl68bcjrqknfv2zkhjczm744q9z-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected