.github: use ubuntu-22.04 for actions

Apparently 'ubuntu-latest' is still 20.04 and today is 2022-10-03,
which seems a bit old!

See: https://github.com/actions/runner-images

.github/workflows/python-app.yml

@@ -12,14 +12,15 @@ on:
 jobs:
   build:
 
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
     - name: Set up Python 3.10
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v4
       with:
         python-version: '3.10'
+        cache: 'pip'
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip