Check cache hit before uploading on Post Setup Node #1346

Description:

Check for a cache hit before uploading.

On a large codebase with a lot of dependencies, the upload can take some time. If you have a lot of concurrent actions, they will all upload the same cache, even if a job that finished earler has already uploaded a cache for the hash.

Justification:

Would save a lot of time, network bandwidth, and trees!

Are you willing to submit a PR?
Yes - I can have go if you think this is feasible/worthwhile!