fix: Card cover image get skretched

[afc163]

🤔 This is a ...

• New feature
• Bug fix
• Site / document update
• Component style update
• TypeScript definition update
• Refactoring
• Code style optimization
• Test Case
• Branch merge
• Other (about what?)

🔗 Related issue link

close #20698

💡 Background and solution

Image max-width 的方案会导致 hover 卡片时边缘依然出现白色边框（这里是需要去掉的）。

cc @zombieJ

• 图片宽度不够不能拉伸。
• Hover 时图片两边不能出现白色边框。

📝 Changelog

Language	Changelog
🇺🇸 English	Fix Card cover image get skretched
🇨🇳 Chinese	修复 Card 封面图片被拉伸的问题。

☑️ Self Check before Merge

• 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

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[codecov]

Codecov Report

Merging #20701 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #20701   +/-   ##
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  Coverage   97.54%   97.54%           
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  Files         295      295           
  Lines        6842     6842           
  Branches     1900     1856   -44     
=======================================
  Hits         6674     6674           
  Misses        168      168

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