Added .NET 10 install in appveyor.yml, as vs2026 is not available.

Author: JanKallman

appveyor8.yml

@@ -3,7 +3,13 @@ branches:
   only:
   - develop8
 configuration: release
-image: Visual Studio 2026
+image: Visual Studio 2022
+install:
+- ps: |
+    Invoke-WebRequest -Uri 'https://dot.net/v1/dotnet-install.ps1' -UseBasicParsing -OutFile "$env:temp\dotnet-install.ps1"
+    & $env:temp\dotnet-install.ps1 -Architecture x64 -Version '10.0.100' -InstallDir "$env:ProgramFiles\dotnet"
+before_build:
+  - cmd: dotnet --version
 init:
 - ps: >-
     Update-AppveyorBuild -Version "8.4.0.$env:appveyor_build_number-$(Get-Date -format yyyyMMdd)-$env:appveyor_repo_branch"