CI: attempt to fix Gitlab 'cobertura' removal

CI: attempt to fix Gitlab 'cobertura' removal

The `cobertura` keyword was deprecated in March¹ and then completely removed on
2022-05-05,² causing all CI pipelines to now fail. This is an attempt to migrate
to the new syntax. More details in
https://gitlab.com/gitlab-org/gitlab/-/issues/361615.

Gitlab: Fixes #2236

¹ https://gitlab.com/gitlab-org/gitlab/-/commit/eae7dfc843783e270607d71c6db0c1ab6a52a8d1
² https://gitlab.com/gitlab-org/gitlab/-/commit/812408bafae328b81652110fc53c6c6b89e3db81#62c40d79aabcb1ce977904c9c748b08045ff0a85