ci: Refactor CI to enable reuse in Virglrenderer CI
This is a re-spin of !12806 (closed) to do some CI infrastructure refactoring (i.e. move out some common variables into a separate file) in order to facilitate the reuse in Virglrenderer CI.
This is a re-spin of !12806 (closed) to do some CI infrastructure refactoring (i.e. move out some common variables into a separate file) in order to facilitate the reuse in Virglrenderer CI.