Appveyor: Try to fix .NET restore

appveyor.yml

@@ -31,6 +31,16 @@ install:
   - ..\DiligentCore\BuildTools\Scripts\appveyor\install.bat
 
 before_build:
+  - $URL = "https://api.github.com/repos/microsoft/winget-cli/releases/latest"
+  - $URL = (Invoke-WebRequest -Uri $URL).Content | ConvertFrom-Json |
+        Select-Object -ExpandProperty "assets" |
+        Where-Object "browser_download_url" -Match '.msixbundle' |
+        Select-Object -ExpandProperty "browser_download_url"
+
+  - Invoke-WebRequest -Uri $URL -OutFile "Setup.msix" -UseBasicParsing
+  - Add-AppxPackage -Path "Setup.msix"
+  - Remove-Item "Setup.msix"
+  - winget install Microsoft.DotNet.SDK.6
   - cd c:\projects\DiligentSamples\BuildTools\FormatValidation
   - validate_format_win.bat
   - cd c:\projects
@@ -42,7 +52,7 @@ before_build:
   - echo add_subdirectory(DiligentSamples) >> CMakeLists.txt
   - echo %PLATFORM%
   - cmake -S . -B ./build -G "Visual Studio 16 2019" -A %PLATFORM%
-  - nuget restore c:\projects\build\DiligentSamples_Test.sln
+  - dotnet restore c:\projects\build\DiligentSamples_Test.sln
 
 build:
   project: c:\projects\build\DiligentSamples_Test.sln