Fix samples CI runs under Python 3.9 / 3.10.

[tseaver]

From PR #476, see 3.9 and 3.10 samples run failures.

The generated noxfile.py files in samples/ don't have those sessions. I believe the correct fix is to add noxfile_config.py to each sample directory, overriding the generated set of Python versions to run.

[tseaver]

The better fix appears to be to refresh each sample's noxfile.py from the (canonical version](https://github.com/GoogleCloudPlatform/python-docs-samples/blob/main/noxfile-template.py).