fix(components): [select] style error in multiple collapseTags

[Fuphoenixes]

fix: [Component] [select] el-select 设置 multiple collapseTags 为 true 时，tag宽度异常

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Description

🤖 Generated by Copilot at 7181c0f

Fix tag width calculation for select component with multiple and collapse-tags props. Modify tagTextStyle in select.vue and add an assertion in select.test.ts.

Related Issue

Fixes #14601 .

Explanation of Changes

🤖 Generated by Copilot at 7181c0f

• Fix a bug where the tag max-width was not calculated correctly when the tags were collapsed in the select component (link)
• Improve the test coverage for the select component with multiple and collapse-tags props (link)

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[github-actions]

🧪 Playground Preview: https://element-plus.run/?pr=14602
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[Fuphoenixes]

@btea 为什么这个pr还没合成功？

[btea]

你好，PR 合并之前还需另一个人同意。其他人暂时可能忙于工作来不及查看，请耐心等待。谢谢你的贡献！