[.Net] update dotnet-ci and dotnet-release to use 8.0.x version when setting up .NET. And enable format check (#3136)

* use 8.0.x versin

* enable format check

* change file header

* apply code format

* add instructions in ci to fix format error

* add comment back

dotnet/sample/AutoGen.BasicSamples/Example15_GPT4V_BinaryDataImageMessage.cs

@@ -50,7 +50,9 @@ public static class Example15_GPT4V_BinaryDataImageMessage
         foreach (string file in Directory.GetFiles(imageResourcePath))
         {
             if (!_mediaTypeMappings.TryGetValue(Path.GetExtension(file).ToLowerInvariant(), out var mediaType))
+            {
                 continue;
+            }
 
             using var fs = new FileStream(file, FileMode.Open, FileAccess.Read);
             var ms = new MemoryStream();