fix(comp:modal): header size should be sm when header has no content

[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?

对话框header的尺寸不符合设计规范

What is the new behavior?

在header有内容的时候尺寸为md，无内容时尺寸为sm

Other information

[idux-bot]

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[codecov]

Codecov Report

Merging #1634 (c4ab17d) into main (97bdafb) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head c4ab17d differs from pull request most recent head 52d3f8a. Consider uploading reports for the commit 52d3f8a to get more accurate results

@@           Coverage Diff           @@
##             main    #1634   +/-   ##
=======================================
  Coverage   92.62%   92.62%           
=======================================
  Files         345      345           
  Lines       32199    32204    +5     
  Branches     3677     3677           
=======================================
+ Hits        29825    29830    +5     
  Misses       2374     2374           

Files Changed	Coverage Δ
packages/components/modal/src/ModalWrapper.tsx	79.79% <100.00%> (+0.26%)	⬆️