build: don't save cache for cache existence check (#1953)
Using `actions/cache@v3` instead of `actions/cache/restore@v3` for the
cache lookup in `setup_ingest` is causing CI to save the cache twice
when there's a cache miss. This is unnecessary, but I'm also a little
concerned it's causing some sort of race condition since I've seen
instances of CI failing to save due to the cache already existing (which
shouldn't be the case on a cache miss).
This PR switches the lookup to a `restore` action to avoid duplicate
ingest cache saving.
#### Testing:
There should only be one "Post Run actions/cache@v3" step in each
`setup_ingest` job when there's a cache miss.
[Here](https://github.com/Unstructured-IO/unstructured/actions/runs/6707740917/job/18227300507)
is an example of a cache miss running with this PR.
