Fix README

Author: zklaus

.github/actions/checkout/README.md

@@ -99,7 +99,7 @@ Please refer to the [release page](https://github.com/actions/checkout/releases/
 
     # Additional refs to fetch. Each ref should be separated with new lines. For
     # example, to fetch all tags: `refs/tags/*:refs/tags/*`
-    # Default: 
+    # Default: ''
     additional-fetch-refs: ''
 
     # Personal access token (PAT) used to fetch the repository. The PAT is configured