[codex] Fix GitLab release fetch dependencies

[lobis]

Summary

• remove the explicit coreutils install from the GitLab release fetch job because alma9-base already ships coreutils-single
• keep the fetch job dependency install to curl and jq so it avoids the package conflict seen on tag pipelines
• add a regression test that fails if a dnf install line reintroduces coreutils

Validation

• bash -n gitlab-ci/fetch_github_release.sh gitlab-ci/publish_artifacts.sh
• go test ./...
• go build ./...