Fix CI caching logic

What does this MR do and why?

We've started getting no space left on device failures because our cache has grown too much

$ du -hs .go/pkg/mod/
11G	.go/pkg/mod/

This MR updates the caching key so that we refresh the cache when we update dependencies and/or update .gitlab-ci.yml

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.