chore(workflow): another try

# 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

@@ -19,19 +19,10 @@ jobs:
         with:
           dotnet-version: 8.0.x
 
-      - name: Diagnose network
-        run: |
-          echo "=== DNS test ==="
-          nslookup api.nuget.org || dig api.nuget.org || echo "DNS failed"
-          echo "=== Curl test (nuget.org) ==="
-          curl -v --connect-timeout 10 https://api.nuget.org/v3/index.json 2>&1 || echo "curl failed"
-          echo "=== Curl test (huawei mirror) ==="
-          curl -v --connect-timeout 10 https://repo.huaweicloud.com/repository/nuget/v3/index.json 2>&1 || echo "curl failed"
-          echo "=== Proxy env ==="
-          env | grep -i proxy || echo "no proxy set"
-      
       - name: Restore dependencies
-        run: dotnet restore --source "https://repo.huaweicloud.com/repository/nuget/v3/index.json"
+        run: dotnet restore
+        env:
+          DOTNET_RESTORE_SOURCES: "https://repo.huaweicloud.com/repository/nuget/v3/index.json"
       
       - name: Build
         run: dotnet build --no-restore --configuration Release