Feature request: restore-only cache usage #149
Description
GitHub's actions/cache defaults to restoring from the cache when the action is invoked, then saving to the cache at the end of the run, but it also has some "sub-actions" – "actions/cache/restore" and "actions/cache/save" – that permit only saving to the cache or only restoring from the cache.
Given Nix's determinism, I can't think of any use for a save-only version of this action, but I could definitely use a restore-only version: given GitHub limits what caches can be accessed based on the branch that triggered the action, I'd rather use the cache space only for my default branch. Having a restore-only version of this action would mean builds on short-lived branches could benefit from the default branch's cache, without using up the limited cache storage with things that I know I'm not likely to need again.