gitlab-ci: Avoid relying on target branch name
When computing the merge base for the linters don't rely on the target
branch name as this is rather fragile. Instead we can just use
$CI_MERGE_REQUEST_TARGET_BRANCH_SHA
.
When computing the merge base for the linters don't rely on the target
branch name as this is rather fragile. Instead we can just use
$CI_MERGE_REQUEST_TARGET_BRANCH_SHA
.