chore: update docfx minimum Python version (#1891)

* chore: update split repo files

* chore: update monorepo script default version

* Revert dropping 3.7 for unit tests as it's still supported

* chore: update sphinx version to 4.5 for monorepo docs build

---------

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

Author: dandhlee

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

@@ -28,7 +28,7 @@ jobs:
     - name: Setup Python
       uses: actions/setup-python@v4
       with:
-        python-version: "3.9"
+        python-version: "3.10"
     - name: Install nox
       run: |
         python -m pip install --upgrade setuptools pip wheel

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

@@ -370,7 +370,7 @@ def docs(session):
     )
 
 
-@nox.session(python="3.9")
+@nox.session(python="3.10")
 def docfx(session):
     """Build the docfx yaml files for this library."""
 

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

@@ -359,7 +359,7 @@ def docs(session):
 
     session.install("-e", ".")
     session.install(
-        "sphinx==4.0.1",
+        "sphinx==4.5.0",
         "alabaster",
         "recommonmark",
     )

synthtool/languages/python_mono_repo.py

@@ -225,7 +225,7 @@ def owlbot_main(package_dir: str) -> None:
         templated_files = gcp.CommonTemplates().py_mono_repo_library(
             relative_dir=f"packages/{package_name}",
             microgenerator=True,
-            default_python_version="3.9",
+            default_python_version="3.10",
             unit_test_python_versions=["3.7", "3.8", "3.9", "3.10", "3.11"],
             system_test_python_versions=["3.8", "3.9", "3.10", "3.11"],
             cov_level=100,