fix(Toast): multiple toasts should show last one

[xiaoyao96]

close #6725

[github-actions]

PR preview has been successfully built and deployed to https://antd-mobile-preview-pr-6729.surge.sh

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.67%. Comparing base (333c6c8) to head (9830dfe).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6729   +/-   ##
=======================================
  Coverage   92.66%   92.67%           
=======================================
  Files         331      331           
  Lines        7170     7176    +6     
  Branches     1756     1759    +3     
=======================================
+ Hits         6644     6650    +6     
  Misses        517      517           
  Partials        9        9           

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