Use current checkout action in example as well

Author: jon-turney

README.md

@@ -7,7 +7,7 @@ e.g.
 
     - run: git config --global core.autocrlf input
 
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
 
     - uses: cygwin/cygwin-install-action@master