message: Add Python 3.9 to build matrix
  This changelist adds Python 3.9 to the build matrix in GitHub Actions, leveraging support for this version of Python in PyBind11 2.7.1.
diff: @@ -89,10 +89,10 @@ jobs:
  python: 3.8
  cmake_config: -G "Visual Studio 16 2019" -A "x64"
  - - name: Windows_VS2022_x64_Python37
  + - name: Windows_VS2022_x64_Python39
  os: windows-2022
  architecture: x64
  - python: 3.8
  + python: 3.9
  cmake_config: -G "Visual Studio 17 2022" -A "x64"
  test_validate: ON
  