Add objectFormat setting to allow init()ing a repo with sha256

README.md

@@ -126,6 +126,11 @@ Please refer to the [release page](https://github.com/actions/checkout/releases/
     # running from unless specified. Example URLs are https://github.com or
     # https://my-ghes-server.example.com
     github-server-url: ''
+
+    # Use the given object format when creating local repository. Specifically, use
+    # 'sha256' to checkout a SHA-256 repository.
+    # Default: null
+    object-format: ''
 ```
 <!-- end usage -->
 
@@ -144,6 +149,7 @@ Please refer to the [release page](https://github.com/actions/checkout/releases/
 - [Checkout pull request on closed event](#Checkout-pull-request-on-closed-event)
 - [Push a commit using the built-in token](#Push-a-commit-using-the-built-in-token)
 - [Push a commit to a PR using the built-in token](#Push-a-commit-to-a-PR-using-the-built-in-token)
+- [Checkout SHA-256 repository](#checkout-sha-256-repository)
 
 ## Fetch only the root files
 
@@ -323,6 +329,14 @@ permissions:
   contents: read
 ```
 
+## Checkout SHA-256 repository
+
+```yaml
+- uses: actions/checkout@v4
+  with:
+    object-format: sha256
+```
+
 # License
 
 The scripts and documentation in this project are released under the [MIT License](LICENSE)