.gitlab-ci.yml: Replace the cobertura tag with coverage_report
Gitlab 15 changed artifacts:reports:cobertura for a slightly more verbose syntax.
https://docs.gitlab.com/ee/ci/yaml/artifacts_reports.html#artifactsreportscobertura-removed
Gitlab 15 changed artifacts:reports:cobertura for a slightly more verbose syntax.
https://docs.gitlab.com/ee/ci/yaml/artifacts_reports.html#artifactsreportscobertura-removed