CI: Fix caching between jobs

fog-aws gem was not installed so Job #19895 failed for b566104d The reason was that caching was configured wrongly so files got cached vertically for each job. After re-configuring the gitlab-runner cache on beluga, caches were lost and resulted in failing builds. This commit configures caching in a way that we define one global cache for all platform pipelines.

Resolves: #8872 (closed)