GitHub Actions seems to have magically switched architectures
without changing their identifiers.
See https://github.com/actions/runner-images/blob/2813ee66cbe85b31a8322ff8967148548b1a5db9/README.md#available-images
Maybe they have more complete documentation elsewhere, but it
seems to be incapable of selecting a runner based on architecture.
(cherry picked from commit df3e92ff96)