更新 CI 工作流中的 .NET 设置，升级至 actions/setup-dotnet@v4

Author: Wybxc

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Setup .NET
-        uses: actions/setup-dotnet@v3
+        uses: actions/setup-dotnet@v4
         with:
           dotnet-version: 8.0.x