ci: use dotnet 9

Author: cnblogs-dudu

.github/workflows/ci.yml

@@ -24,9 +24,9 @@ jobs:
     steps: 
     - uses: actions/checkout@v3
     - name: Setup .NET
-      uses: actions/setup-dotnet@v2
+      uses: actions/setup-dotnet@v4
       with:
-        dotnet-version: 7.0.x
+        dotnet-version: '9'
     - if: contains(matrix.runs-on, 'macOS') || contains(matrix.runs-on, 'ubuntu')
       env:
         MINVERVERSIONOVERRIDE: ${{ secrets.MINVER_VERSION }}