docs: fix broken Ubuntu 24.04 repository URL in EN install guide

[muzimu217]

问题

英文安装指南的 Ubuntu 24.04 小节使用的存储库地址为
https://ci.deepin.com/repo/obs/linglong:/CI:/release/xUbuntu_24.04/，该路径当前返回 404：

$ curl -o /dev/null -s -w '%{http_code}\n' https://ci.deepin.com/repo/obs/linglong:/CI:/release/xUbuntu_24.04/
404
$ curl -o /dev/null -s -w '%{http_code}\n' https://ci.deepin.com/repo/obs/linglong:/CI:/release/Ubuntu_24.04/
200

同一 URL 在中文指南中已由 #1865 修正为 Ubuntu_24.04/，但英文版遗漏。
全仓搜索 xUbuntu 仅剩这一处；同文档 Ubuntu 25.04 / 25.10 小节使用的
Ubuntu_25.04/、Ubuntu_25.10/ 均可正常访问（200）。

修改

将 docs/pages/en/guide/start/install.md 中 Ubuntu 24.04 的存储库地址
xUbuntu_24.04/ 改为 Ubuntu_24.04/，与中文指南 #1865 保持一致。

单行改动，不影响其他发行版小节。

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Welcome @muzimu217! It looks like this is your first PR to OpenAtom-Linyaps/linyaps 🎉

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