fix(form): fix addonAfter style error

[chenshuai2144]

close #5309

[github-actions]

🎊 PR Preview has been successfully built and deployed to https://pro-components-preview-pr-5312.surge.sh

[codecov]

Codecov Report

Merging #5312 (6c08f7a) into master (2058bf4) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #5312   +/-   ##
=======================================
  Coverage   99.73%   99.73%           
=======================================
  Files         206      206           
  Lines        6809     6809           
  Branches     2482     2482           
=======================================
  Hits         6791     6791           
  Misses         18       18           

Impacted Files	Coverage Δ
packages/form/src/components/FormItem/index.tsx	100.00% <ø> (ø)

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