this derivation will be built:
  /nix/store/lvqkig5b3gzjh30aky62lpaabsxzj48f-interpolate-conformance.drv
bld4: building lvqkig5b3gzjh30aky62lpaabsxzj48f-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected