CodeQL: use os matrix with explicitly stated versions instead of just latest

.github/workflows/codeql-analysis.yml

@@ -7,7 +7,7 @@ on:
 jobs:
   analyze:
     name: Analyze
-    runs-on: ubuntu-latest
+    
     permissions:
       actions: read
       contents: read
@@ -16,9 +16,12 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
+        os: [ 'ubuntu-20.04', 'ubuntu-22.04']
         language: [ 'python' ]
         python-version: ['3.8', '3.10']
 
+    runs-on: ${{ matrix.os }}
+
     steps:
     - name: Checkout repository
       uses: actions/checkout@v2