chore(python): use python 3.9 for docs build (#1713)

Author: parthea

synthtool/gcp/templates/python_library/.github/workflows/docs.yml

@@ -12,7 +12,7 @@ jobs:
     - name: Setup Python
       uses: actions/setup-python@v4
       with:
-        python-version: "{{ default_python_version }}"
+        python-version: "3.9"
     - name: Install nox
       run: |
         python -m pip install --upgrade setuptools pip wheel
@@ -28,7 +28,7 @@ jobs:
     - name: Setup Python
       uses: actions/setup-python@v4
       with:
-        python-version: "{{ default_python_version }}"
+        python-version: "3.9"
     - name: Install nox
       run: |
         python -m pip install --upgrade setuptools pip wheel

synthtool/gcp/templates/python_library/.kokoro/docker/docs/Dockerfile

@@ -60,16 +60,16 @@ RUN apt-get update \
   && rm -rf /var/lib/apt/lists/* \
   && rm -f /var/cache/apt/archives/*.deb
 
-###################### Install python 3.8.11
+###################### Install python 3.9.13
 
-# Download python 3.8.11
-RUN wget https://www.python.org/ftp/python/3.8.11/Python-3.8.11.tgz
+# Download python 3.9.13
+RUN wget https://www.python.org/ftp/python/3.9.13/Python-3.9.13.tgz
 
 # Extract files
-RUN tar -xvf Python-3.8.11.tgz
+RUN tar -xvf Python-3.9.13.tgz
 
-# Install python 3.8.11
-RUN ./Python-3.8.11/configure --enable-optimizations
+# Install python 3.9.11
+RUN ./Python-3.9.13/configure --enable-optimizations
 RUN make altinstall
 
 ###################### Install pip

synthtool/gcp/templates/python_library/noxfile.py.j2

@@ -340,7 +340,7 @@ 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."""