fix: 修复swiper-item 添加class不生效问题

[PlutoCA]

#1369

原生小程序是支持给swiper-item 添加class的，有场景可能需要动态操作它的样式

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[yesmeck]

需要在 packages/remax-cli 下跑下 yarn test -u 然后提交下变更。

[codecov]

Codecov Report

Merging #1371 (07d4816) into master (24a360d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1371   +/-   ##
=======================================
  Coverage   95.39%   95.39%           
=======================================
  Files         350      350           
  Lines        3780     3780           
  Branches      543      543           
=======================================
  Hits         3606     3606           
  Misses        171      171           
  Partials        3        3           

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