Appveyor: Try to fix .NET restore

BuildTools/Scripts/appveyor/install-dotnet.py

@@ -0,0 +1,34 @@
+import requests
+import subprocess
+import sys
+
+DOTNET_INSTALL_SCRIPT_URL = "https://dotnet.microsoft.com/download/dotnet/scripts/v1/dotnet-install.ps1"
+
+DOTNET_INSTALL_SCRIPT_PATH = "dotnet-install.ps1"
+
+DOTNET_INSTALL_SCRIPT_ARGS = [
+    "-Channel", "6.0.1xx",
+    "-Quality", "preview"
+]
+
+def execute(command):
+    process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
+
+    while True:
+        nextline = process.stdout.readline()
+        if not nextline and process.poll() is not None:
+            break
+        print(line.decode(), end='')
+
+
+def main():
+    response = requests.get(DOTNET_INSTALL_SCRIPT_URL)
+    with open(DOTNET_INSTALL_SCRIPT_PATH, 'wb') as script_file:
+        script_file.write(response.content)
+
+    command = ["powershell.exe", "-ExecutionPolicy", "Bypass", "-File", DOTNET_INSTALL_SCRIPT_PATH] + DOTNET_INSTALL_SCRIPT_ARGS
+    execute(command)
+
+
+if __name__ == "__main__":
+    main()

appveyor.yml

@@ -32,6 +32,10 @@ install:
 
 before_build:
   - cd c:\projects\DiligentSamples\BuildTools\FormatValidation
+  - cd c:\projects\DiligentSamples\BuildTools\Scripts\appveyor
+  - python -m pip install requests
+  - python install-dotnet.py
+  - cd c:\projects
   - validate_format_win.bat
   - cd c:\projects
   - echo cmake_minimum_required(VERSION 3.6) > CMakeLists.txt
@@ -42,7 +46,7 @@ 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