build: streamline ci (#1909)
Updated CI to shave time off in some conditions with no real downside.
- When the base cache already exists, we don't download it during setup,
and we skip all other steps as well.
- During ingest setup, we check if the ingest cache exists before
downloading the base cache, and if the ingest cache already exists, we
skip everything else.
- `check-deps` doesn't have to wait on `setup` or download a cache, as
the dependencies aren't needed, only `pip`.
