Remove the builtin:checkout docs (#643)

Follow-up to https://gitea.com/gitea/runner/pulls/1407, which removes the runner's builtin actions. Drops `builtin:checkout` from the develop runner docs and the current comparison page, and lists the removal under the 6.0 breaking changes. Versioned docs keep it, as released runners still ship it, with their `builtin-actions.md` links pinned to the latest 4.x and 5.x tags since the file leaves runner main.

Co-authored-by: Lunny Xiao <[email protected]>
Reviewed-on: https://gitea.com/gitea/docs/pulls/643
Reviewed-by: Lunny Xiao <[email protected]>
Co-authored-by: silverwind <[email protected]>

runner-docs/index.md

@@ -23,7 +23,6 @@ Jobs need these tools wherever steps run, in the job image or on the host:
 
 - `bash` or `sh` for `run` steps, or `pwsh` or `powershell` on Windows.
 - `node` for JavaScript actions and `hashFiles()`.
-- `git` 2.34.1 or later for [`builtin:checkout`](jobs.md#built-in-checkout), plus `git-lfs` for its `lfs` input and `ssh` for its `ssh-key` input.
 
 ## Where jobs run
 

runner-docs/jobs.md

@@ -68,10 +68,6 @@ Setup actions such as `actions/setup-go` install tools in `/opt/hostedtoolcache`
 
 With `none`, include tools in the job image at `/opt/hostedtoolcache/<tool>/<version>/<arch>`. Place an empty `<arch>.complete` file next to the directory. The `-full` variant of the [runner images](https://gitea.com/gitea/runner-images) includes its tools this way.
 
-## Built-in checkout
-
-`uses: builtin:checkout` checks out the repository like `actions/checkout`. It does not download an action or require Node in the job image. It runs `git` in the job. See [Requirements](index.md#requirements) and the inputs listed in [builtin-actions.md](https://gitea.com/gitea/runner/src/branch/main/docs/builtin-actions.md).
-
 ## Secrets
 
 The runner masks secrets and `::add-mask::` values in job logs, job summaries, and the names of containers it creates. The runner does not send job outputs that contain a secret. A `needs.<job>.outputs.<name>` expression that reads such an output is empty.

runner-docs/upgrade.md

@@ -14,6 +14,10 @@ sudo systemctl start gitea-runner
 
 Stopping the runner cancels running jobs unless `runner.shutdown_timeout` gives them time to finish. The runner logs a warning for unknown configuration keys and ignores them. Run `gitea-runner config generate` to list all configuration options.
 
+## Breaking changes in 6.0
+
+- **`builtin:checkout` is removed.** Steps that use it fail. Use `actions/checkout` or a lightweight action such as [`taiki-e/checkout-action`](https://github.com/taiki-e/checkout-action).
+
 ## Breaking changes in 5.0
 
 - **Git 2.34.1 or later is required** on the runner and in job images that use `builtin:checkout`.