fix(components): [cascader] form nested causing clear icon invalid

[btea]

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fix #16059

[github-actions]

[github-actions]

🧪 Playground Preview: https://element-plus.run/?pr=16068
Please comment the example via this playground if needed.

[kooriookami]

I think cascader can be refactored with select.

[btea]

I think cascader can be refactored with select.

Are there any refactoring plans in the short term?

[kooriookami]

I think cascader can be refactored with select.

Are there any refactoring plans in the short term?

May be few months, you can merge this PR first.