Replace actions/checkout with instance git clone (github.com unreachable from runner)

.gitea/workflows/build.yaml

@@ -10,8 +10,16 @@ jobs:
   build:
     runs-on: windows-latest
     steps:
+      # runner 到 github.com 网络不稳定，不使用 actions/checkout@v4，
+      # 改为直接从本 Gitea 实例克隆代码
       - name: Checkout
-        uses: actions/checkout@v4
+        shell: pwsh
+        env:
+          GITEA_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          $url = "${{ gitea.server_url }}/${{ github.repository }}.git" -replace '^https://', "https://x-access-token:$env:GITEA_TOKEN@"
+          git clone $url .
+          git checkout ${{ github.sha }}
 
       - name: Install dependencies
         run: npm ci