GitHub Actions seems to have magically switched architectures
without changing their identifiers.
See 2813ee66cb/README.md (available-images)
Maybe they have more complete documentation elsewhere, but it
seems to be incapable of selecting a runner based on architecture.
This avoids polluting nixComponents with things that aren't our
components.
Fixes the extraction of passthru tests, which failed for boehmgc
which had many irrelevant ones anyway.