Update publications.yml to respect new GitHub Actions

please see https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/ and actions/checkout#1047

.github/workflows/publications.yml

@@ -11,7 +11,7 @@ jobs:
 
     steps:
       - name: checkout repo content
-        uses: actions/checkout@v2 # checkout the repository content to github runner.
+        uses: actions/checkout@v3 # checkout the repository content to github runner.
 
       - name: setup python
         uses: actions/setup-python@v2