fix(dockerfile): use sjtu mirror for install

Signed-off-by: 王韵晨520370910012 <mac-wang@sjtu.edu.cn>

Dockerfile

@@ -2,6 +2,13 @@
 
 FROM focs.ji.sjtu.edu.cn:5000/gitea/runner-images:ubuntu-latest-slim
 
+# use sjtug mirror for faster download
+RUN rm -rf /etc/apt/sources.list.d/* && cat <<EOF > /etc/apt/sources.list
+deb http://mirror.sjtu.edu.cn/debian bookworm main
+deb http://mirror.sjtu.edu.cn/debian-security bookworm-security main
+deb http://mirror.sjtu.edu.cn/debian bookworm-updates main
+EOF
+
 RUN apt-get update && \
     apt-get install -y sudo python3-minimal pipx git && \
     apt-get clean && \