this derivation will be built:
  /nix/store/m8l42l9f0ajby9l4wivhqwjmi0w36w3r-interpolate-conformance.drv
bld4: building m8l42l9f0ajby9l4wivhqwjmi0w36w3r-interpolate-conformance.drv
10 cases: Nix interpolate == Python interpolate == expected