Allow optionally testing for `cache-hit` without restoring old cache

[ankith26]

First of all, thanks to the maintainers and contributors who keep this project up, which helps make CI cache handling simple! 🥳

Use case

I have a build matrix with 5 jobs, that need to access (but not write) a common cache. To update this cache, I have a job that this matrix depends on (that runs before it). This job restores cache and populates cache on a cache miss, so that subsequent jobs can use it.

This works, but there is an unneeded step of restoring cache in my first job, when all I want to do is to just test for a cache miss, rebuild in that case and upload new cache.

Proposal

There should be an input dry-run/test-cache/no-pull/[anything-else-here] (yes naming things is hard😅) that should control whether the cache is pulled initially (should default to yes). Then cache-hit should be set accordingly, and post cache step should run normally

[Exelord]

I have exactly the same case. That would be really welcome feature!

[kotewar]

Closing this and tracking the same in https://github.com/actions/cache/issues/901