chore(workflow): 配置华为云和腾讯云NuGet镜像以提升包恢复速度

# 华为云和腾讯云的 NuGet 镜像配置
- 替换原有的网络诊断步骤为NuGet镜像配置
- 添加华为云和腾讯云的NuGet源到nuget.config文件
- 修改dotnet restore命令使用配置文件而非直接指定源地址

.gitea/workflows/dotnet.yml

@@ -19,8 +19,22 @@ jobs:
         with:
           dotnet-version: 8.0.x
       
+      # 华为云和腾讯云的 NuGet 镜像配置
+      - name: Configure NuGet mirror
+        run: |
+          cat > nuget.config << 'EOF'
+          <?xml version="1.0" encoding="utf-8"?>
+          <configuration>
+            <packageSources>
+              <clear />
+              <add key="huawei-mirror" value="https://repo.huaweicloud.com/repository/nuget/v3/index.json" />
+              <add key="tencent" value="https://mirrors.cloud.tencent.com/nuget/" />
+            </packageSources>
+          </configuration>
+          EOF
+
       - name: Restore dependencies
-        run: dotnet restore --source "https://repo.huaweicloud.com/repository/nuget/v3/index.json"
+        run: dotnet restore
       
       - name: Build
         run: dotnet build --no-restore --configuration Release