fix(modal): fix Dropdown.Button not correctly rendered in Modal footer

[Map1en]

[中文版模板 / Chinese template]

🤔 This is a ...

• New feature
• Bug fix
• Site / documentation update
• Demo update
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• TypeScript definition update
• Bundle size optimization
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🔗 Related issue link

close #30317

💡 Background and solution

📝 Changelog

Language	Changelog
🇺🇸 English	Fix Dropdown.Button broken style when inside Modal footer.
🇨🇳 Chinese	修正 Modal footer 放置里 Dropdown.Button 的样式错乱问题。

☑️ Self Check before Merge

⚠️ Please check all items below before review. ⚠️

• Doc is updated/provided or not needed
• Demo is updated/provided or not needed
• TypeScript definition is updated/provided or not needed
• Changelog is provided or not needed

[github-actions]

[codecov]

Codecov Report

Merging #30328 (b12c505) into master (4951b59) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master    #30328   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          397       397           
  Lines         7522      7522           
  Branches      2105      2105           
=========================================
  Hits          7522      7522           

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