Fix code comment to mention py3.6

.github/workflows/build_and_test.yaml

@@ -12,7 +12,7 @@ jobs:
     # assuming that any pull requests from the same repo are infra changes.
     if: github.event.pull_request.head.repo.full_name != github.repository
 
-    # As long as we need Python 3.8 here in the test, we can only use up to Ubuntu 20
+    # As long as we need Python 3.6 here in the test, we can only use up to Ubuntu 20
     # See https://raw.githubusercontent.com/actions/python-versions/main/versions-manifest.json
     runs-on: ubuntu-20.04
     name: 'Build and Test / Python ${{ matrix.python-version-short }}'