Add workaround for failing 'dotnet pack'

Caused by an unintentional breaking change in .NET SDK v7.0.200, which the latest AppVeyor image uses

Author: bkoelman

appveyor.yml

@@ -1,6 +1,8 @@
 image:
   - Ubuntu2004
-  - Visual Studio 2022
+  # Downgrade to workaround error NETSDK1194 during 'dotnet pack': The "--output" option isn't supported when building a solution.
+  # https://stackoverflow.com/questions/75453953/how-to-fix-github-actions-dotnet-publish-workflow-error-the-output-option-i
+  - Previous Visual Studio 2022
 
 version: '{build}'