GitHub action for rebuilding cache

Rebuilding the cache is more painful than needed, especially for new contributors, see e.g. https://github.com/CarloLucibello/GraphNeuralNetworks.jl/pull/253
First of all, you have to know you have to rebuild the cache, then you have to install the exact julia version used for the cache (also the patch number matters) and finally do the rebuild.

I was wondering if there is some way to configure a github action to do the whole thing, i.e. check for changes in the cache and do the rebuild only if there are any.