Manually install .net9

Author: twcclegg

appveyor.yml

@@ -22,6 +22,10 @@ pull_requests:
 branches:
   only:
     - main
+install:
+- ps: |
+    Invoke-WebRequest -Uri 'https://dot.net/v1/dotnet-install.ps1' -UseBasicParsing -OutFile "$env:temp\dotnet-install.ps1"
+    & $env:temp\dotnet-install.ps1 -Architecture x64 -Version '9.0.100' -InstallDir "$env:ProgramFiles\dotnet"
 before_build:
   - dotnet restore csharp -s https://api.nuget.org/v3/index.json
   - ps: Compress-Archive -Path "resources\geocoding\*" -DestinationPath "resources\geocoding.zip"