Switching to latest action versions.

Author: chsou

.github/workflows/python-publish.yml

@@ -18,11 +18,11 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - name: Set up Python
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v5
       with:
-        python-version: '3.x'
+        python-version: '3.9'
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip