Upgrade dotnet version

Author: lph-hhh

.github/workflows/main.yml

@@ -97,7 +97,7 @@ jobs:
     - name: Setup .NET
       uses: actions/setup-dotnet@v3
       with:
-        dotnet-version: 7.x
+        dotnet-version: 9.x
 
     - name: Install DocFX
       run: dotnet tool update -g docfx