fix(module:breadcrumb): patch last-child's style indule a is included

[stygian-desolator]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/NG-ZORRO/ng-zorro-antd/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: N/A
close #5942

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[zorro-bot]

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[codecov]

Codecov Report

Merging #5994 into master will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #5994   +/-   ##
=======================================
  Coverage   89.93%   89.93%           
=======================================
  Files         465      465           
  Lines       14044    14044           
  Branches     2307     2307           
=======================================
+ Hits        12630    12631    +1     
- Misses        865      866    +1     
+ Partials      549      547    -2     

Impacted Files	Coverage Δ
components/table/src/table-data.service.ts	78.46% <0.00%> (-6.16%)	⬇️
components/time-picker/time-holder.ts	95.78% <0.00%> (+1.05%)	⬆️
components/tabs/tab-nav-bar.component.ts	82.33% <0.00%> (+1.41%)	⬆️

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[wenqi73]

Thanks, @stygian-desolator !