🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

Author: gcf-owl-bot[bot]

.github/workflows/unittest.yml

@@ -5,7 +5,7 @@ on:
 name: unittest
 jobs:
   unit:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     strategy:
       matrix:
         python: ['3.6', '3.7', '3.8', '3.9', '3.10', '3.11']