chore(python): update release script dependencies [autoapprove] (#469)

* chore(python): update release script dependencies

Source-Link: googleapis/synthtool@25083af
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:e6cbd61f1838d9ff6a31436dfc13717f372a7482a82fc1863ca954ec47bff8c8

* 🦉 Updates from OwlBot post-processor

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

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>
Co-authored-by: Anthonios Partheniou <partheniou@google.com>

packages/google-cloud-python-speech/noxfile.py

@@ -272,7 +272,7 @@ def cover(session):
     session.run("coverage", "erase")
 
 
-@nox.session(python=DEFAULT_PYTHON_VERSION)
+@nox.session(python="3.9")
 def docs(session):
     """Build the docs for this library."""
 
@@ -298,7 +298,7 @@ def docs(session):
     )
 
 
-@nox.session(python=DEFAULT_PYTHON_VERSION)
+@nox.session(python="3.9")
 def docfx(session):
     """Build the docfx yaml files for this library."""