ci: support both apt sources formats for mirror switching

Update the CI workflow to handle both the legacy sources.list format
and the new ubuntu.sources format when switching to Tsinghua mirrors

.gitea/workflows/build.yml

@@ -36,8 +36,13 @@ jobs:
 
       - name: Install build tools
         run: |
+          if [ -f /etc/apt/sources.list.d/ubuntu.sources ]; then
+            sudo sed -i 's|http://archive.ubuntu.com/ubuntu|https://mirrors.tuna.tsinghua.edu.cn/ubuntu|g' /etc/apt/sources.list.d/ubuntu.sources
+            sudo sed -i 's|http://security.ubuntu.com/ubuntu|https://mirrors.tuna.tsinghua.edu.cn/ubuntu|g' /etc/apt/sources.list.d/ubuntu.sources
+          else
             sudo sed -i 's|http://archive.ubuntu.com|https://mirrors.tuna.tsinghua.edu.cn|g' /etc/apt/sources.list
             sudo sed -i 's|http://security.ubuntu.com|https://mirrors.tuna.tsinghua.edu.cn|g' /etc/apt/sources.list
+          fi
           sudo apt-get update && sudo apt-get install -y gcc
 
       - name: Download dependencies