fix: trim whitespace from command in ExecComposer method

[HynoR]

What this PR does / why we need it?

fix #12285

问题在网站-PHP-Composer

Summary of your change

对最后composer拼接命令进行trimspace清理 避免多余空格

后期会给这个小模块前端和后端做对齐设计，比如自定义命令的判断和镜像源选择，目前发现迷惑性的东西挺多

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• Made sure tests are passing and test coverage is added if needed.
• Made sure commit message follow the rule of Conventional Commits specification.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed.

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