Fix adding duplicate paths to PATH during installation

[wanzzhehe]

修复可能导致PATH重复添加的问题。

[waruqi]

重复添加会有什么问题？

[Issues-translate-bot]

Bot detected the issue body's language is not English, translate it automatically.

---

What are the problems with repeated additions?

[wanzzhehe]

主要是：

1. 减少对环境变量的改动
2. 可能与某些自定义脚本冲突
3. 难看，并且其它软件也这么搞的话PATH会更难看而且过长。

重点解释下2，由于xmake安装脚本会自动修改.bashrc等配置文件，并将修改放在文件最末尾，重复添加PATH就可能导致一些重名工具使用时使用了错误的工具。

[Issues-translate-bot]

Bot detected the issue body's language is not English, translate it automatically.

---

mainly:

1. Reduce changes to environment variables
2. May conflict with some custom scripts
3. It is ugly, and if other software does this, PATH will be even more ugly and too long.

Focus on explanation 2. Since the xmake installation script will automatically modify configuration files such as .bashrc and place the modifications at the end of the file, repeatedly adding PATH may cause some tools with the same name to use the wrong tool.

[waruqi]

目前的改动，两个 ci 会 break

https://github.com/xmake-io/xmake/actions/runs/9094494730/job/25038090326?pr=5108

[wanzzhehe]

我的锅，倒是其他是怎么成功的（

应该用逻辑或的。

[Issues-translate-bot]

Bot detected the issue body's language is not English, translate it automatically.

---

My fault, but how others succeeded (

Logical OR should be used.

[waruqi]

thanks