Update the actions/checkout action used by the Github workflows.

The workflows currently use `actions/checkout@v3` which used node
version 16.  This results in a warning that Node.js 16 actions are
deprecated.  So this updates to `actions/checkout@v4`.

.github/workflows/linter.yml

@@ -17,7 +17,7 @@ jobs:
     container:
       image: perl:5.34
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: perl -V
         run: perl -V
       - name: Install dependencies