Update our CI config according to recent gitlab changes
Clarification and motivation
According to @rvem the following changes can be useful for us:
Apart from that I have found tezos/tezos#796 (closed) (which refers to tezos/tezos#727 (closed)).
Acceptance criteria
Our CI is improved according to the aforementioned changes. If @rvem finds something else that can be useful, we should take that into account as well.
Edited by Ivan Gromakovskii