fix(ci): use composite actions for Go build cache

[tie]

This PR switches from actions/setup-go cache (see actions/setup-go#228) to explicit actions/cache since the former does not allow specifying cache key or at least a key prefix. This is an issue when multiple distinct jobs and workflows use Go cache for different purposes (e.g. run tests, install tools and build docs) and therefore sharing it under the same key makes no sense (and, in fact, breaks caching since the results have to be recomputed).