AppVeyor: Update to VS 2022 image, prepare for Python 3.11

This commit updates the AppVeyor configuration to use the Visual Studio 2022 image, and prepares for Python 3.11 support.

AppVeyor needs to add Python 3.11 to their images before the Python 3.11 jobs can be uncommented.

The feature request can be tracked here: appveyor/ci#3844

appveyor.yml

@@ -1,8 +1,10 @@
 version: 1.0.{build}
-image: Visual Studio 2019
+image: Visual Studio 2022
 
 environment:
   matrix:
+#  - python: 311       # Blocked by https://github.com/appveyor/ci/issues/3844
+#  - python: 311-x64
   - python: 310
   - python: 310-x64
   - python: 39