fix(comp:date-picker): panel header font-size not right

[sallerli1]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines
• Tests for the changes have been added/updated or not needed
• Docs and demo have been added/updated or not needed

What is the current behavior?

日期面板中年月选择的font-size不生效

What is the new behavior?

修复以上问题

Other information

[idux-bot]

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[codecov]

Codecov Report

Merging #1640 (4f74640) into main (97bdafb) will not change coverage.
The diff coverage is n/a.

❗ Current head 4f74640 differs from pull request most recent head 84596d7. Consider uploading reports for the commit 84596d7 to get more accurate results

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  Coverage   92.62%   92.62%           
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  Files         345      345           
  Lines       32199    32199           
  Branches     3677     3677           
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  Hits        29825    29825           
  Misses       2374     2374