Gitea Runner 5.0.0 expands checkout and requires Git 2.34.1

Gitea Runner 5.0.0 expands builtin:checkout with support for SSH settings, LFS, submodules, sparse checkout, partial clones, persisted credentials, and ref and commit outputs. The runner now uses the Git CLI to download actions and reusable workflows, adding SHA-256 repository support and faster full action clones. Git 2.34.1 or later is required, while jobs without runs-on now fail instead of falling back to runner.default_image.