ci: run samples under Python 3.9 / 3.10

[tseaver]

Refresh each sample's noxfile via:

$ for noxfile in samples/*/noxfile.py; do
    echo "Refreshing $noxfile";
    wget -O $noxfile https://github.com/GoogleCloudPlatform/python-docs-samples/raw/main/noxfile-template.py
    echo "Blackening samples for $noxfile"
    nox -f $noxfile -s blacken
done

Closes #477.