checkInputs used to be added to nativeBuildInputs. Now we have
nativeCheckInputs to do that instead. Doing this treewide change allows
to keep hashes identical to before the introduction of
nativeCheckInputs.
One significant use case is adding `passthru.tests` to setup-hooks,
and help increase test coverage for mission-critical setup-hooks.
As `meta`, `passthru` doesn't go into the build script directly.
However, passing an empty set to `passthru` breaks nixpkgs-review
and OfBorg tests, so pass it only when specified.
