Update Python version to 3.13 in workflow

Author: cornelius-koepp

.github/workflows/openknx-oam-check.yml

@@ -86,7 +86,7 @@ jobs:
       - name: Install Python
         uses: actions/setup-python@v5
         with:
-          python-version: '3.8'
+          python-version: '3.13'
 
       - name: Install PlatformIO
         run: |