tools: github actions: update python versions to amatch available ver…

…sion on ubuntu-22.04 runners

- https://raw.githubusercontent.com/actions/python-versions/main/versions-manifest.json

.github/workflows/ci.yml

@@ -5,7 +5,7 @@ jobs:
     runs-on: ubuntu-22.04
     strategy:
       matrix:
-        python-version: ['3.6', '3.7', '3.8', '3.9']
+        python-version: ['3.6.15', '3.7.17', '3.8.18', '3.9.18']
     name: python
     steps:
       - name: Checkout