Fix and update CI configuration

Specify the latest Ubuntu runner and Python version.

.github/workflows/validate.yaml

@@ -4,20 +4,21 @@ on: push
 
 jobs:
   validate:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
       - name: Checkout this repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Setup Python
-        uses: actions/setup-python@v3
+        uses: actions/setup-python@v5
         with:
           python-version: 3.10.4
           cache: 'pip'
 
       - name: Install preprequisites
         run: |
           python -m pip install --upgrade pip
+          pip install pyyaml==5.3.1
           pip install --upgrade opera-tosca-parser
 
       - name: Run validation script