fix!: use the git CLI for action clones and make builtin:checkout match actions/checkout (#1277)

The runner now uses the `git` command line instead of go-git to download actions and reusable workflows. go-git had recurring bugs and does not support SHA-256 repositories, and full clones of actions are several times faster.

`builtin:checkout` now runs `git` where the job runs and behaves like `actions/checkout`:

1. A branch is checked out as a local branch tracking `origin`, tag and pull request runs keep their ref, and a triggering tag that moved fails the step.
1. Later steps can fetch and push with the persisted token or SSH key.
1. It supports the `ssh-*`, `lfs`, `submodules`, `sparse-checkout`, `filter`, `fetch-tags`, `clean`, `persist-credentials`, `show-progress` and `set-safe-directory` inputs and the `ref` and `commit` outputs.
1. SHA-256 repositories work for actions, reusable workflows and `builtin:checkout`.

Git keeps the token off its command line, ignores `GIT_DIR` and similar variables inherited by the runner, and keeps action files LF regardless of `core.autocrlf`. A cancelled job lets git remove its lock files.

This is a breaking change: the runner needs Git 2.34.1 or newer on its `PATH`, and so do job images that use `builtin:checkout`. The official runner images include it.

Fixes: https://gitea.com/gitea/runner/issues/1077
Fixes: https://gitea.com/gitea/runner/issues/1267
Fixes: https://gitea.com/gitea/runner/issues/1279
Fixes: https://gitea.com/gitea/runner/issues/1284
Fixes: https://gitea.com/gitea/runner/issues/1285
Co-authored-by: silverwind <[email protected]>
Co-authored-by: silverwind <[email protected]>
Co-authored-by: Lunny Xiao <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1277
Reviewed-by: Lunny Xiao <[email protected]>
Reviewed-by: silverwind <[email protected]>
Co-authored-by: bircni <[email protected]>

README.md

@@ -4,7 +4,19 @@
 
 ### Prerequisites
 
-Docker Engine Community version is required for docker mode. To install Docker CE, follow the official [install instructions](https://docs.docker.com/engine/install/).
+On the runner:
+
+- `git` 2.34.1 or newer on `PATH`, to download actions and reusable workflows.
+- `docker` or `podman` with `podman.socket` enabled, for docker mode, Docker actions and `docker://` steps. To install Docker CE, follow the official [install instructions](https://docs.docker.com/engine/install/).
+
+Where steps run, in the job image or on the runner in host mode:
+
+- `bash` or `sh` for `run` steps, `pwsh` or `powershell` on a Windows host.
+- `node` for JavaScript actions and `hashFiles()`.
+- `git` 2.34.1 or newer for [`builtin:checkout`](docs/builtin-actions.md).
+- `git-lfs` and `ssh` for `builtin:checkout`, only when its `lfs` or `ssh-key` input is used.
+
+Kubernetes mode needs [a few more tools](docs/kubernetes.md) in job images.
 
 ### Download pre-built binary