chore(python): use ubuntu 22.04 in docs image (#1422)

* chore(deps): update dependency ubuntu to v22

* ci: install python 3.8

Co-authored-by: Anthonios Partheniou <partheniou@google.com>

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

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from ubuntu:20.04
+from ubuntu:22.04
 
 ENV DEBIAN_FRONTEND noninteractive
 
@@ -60,8 +60,24 @@ RUN apt-get update \
   && rm -rf /var/lib/apt/lists/* \
   && rm -f /var/cache/apt/archives/*.deb
 
+###################### Install python 3.8.11
+
+# Download python 3.8.11
+RUN wget https://www.python.org/ftp/python/3.8.11/Python-3.8.11.tgz
+
+# Extract files
+RUN tar -xvf Python-3.8.11.tgz
+
+# Install python 3.8.11
+RUN ./Python-3.8.11/configure --enable-optimizations
+RUN make altinstall
+
+###################### Install pip
 RUN wget -O /tmp/get-pip.py 'https://bootstrap.pypa.io/get-pip.py' \
-  && python3.8 /tmp/get-pip.py \
+  && python3 /tmp/get-pip.py \
   && rm /tmp/get-pip.py
 
+# Test pip
+RUN python3 -m pip
+
 CMD ["python3.8"]