chore(python): use python 3.10 for docs build (#1989)

* chore(python): fix docs build

* upgrade python 3.9; add python 3.10

* remove python 3.9; use python 3.10 for docs build

* address review feedback

* clarify comment

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

@@ -40,7 +40,6 @@ RUN apt-get update \
     libssl-dev \
     libsqlite3-dev \
     portaudio19-dev \
-    python3-distutils \
     redis-server \
     software-properties-common \
     ssh \
@@ -60,18 +59,22 @@ RUN apt-get update \
   && rm -rf /var/lib/apt/lists/* \
   && rm -f /var/cache/apt/archives/*.deb
 
-###################### Install python 3.9.13
 
-# Download python 3.9.13
-RUN wget https://www.python.org/ftp/python/3.9.13/Python-3.9.13.tgz
+###################### Install python 3.10.14 for docs/docfx session
+
+# Download python 3.10.14
+RUN wget https://www.python.org/ftp/python/3.10.14/Python-3.10.14.tgz
 
 # Extract files
-RUN tar -xvf Python-3.9.13.tgz
+RUN tar -xvf Python-3.10.14.tgz
 
-# Install python 3.9.13
-RUN ./Python-3.9.13/configure --enable-optimizations
+# Install python 3.10.14
+RUN ./Python-3.10.14/configure --enable-optimizations
 RUN make altinstall
 
+RUN python3.10 -m venv /venv
+ENV PATH /venv/bin:$PATH
+
 ###################### Install pip
 RUN wget -O /tmp/get-pip.py 'https://bootstrap.pypa.io/get-pip.py' \
   && python3 /tmp/get-pip.py \
@@ -84,4 +87,4 @@ RUN python3 -m pip
 COPY requirements.txt /requirements.txt
 RUN python3 -m pip install --require-hashes -r requirements.txt
 
-CMD ["python3.8"]
+CMD ["python3.10"]

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

@@ -355,7 +355,7 @@ def cover(session):
     session.run("coverage", "erase")
 
 
-@nox.session(python="3.9")
+@nox.session(python="3.10")
 def docs(session):
     """Build the docs for this library."""