fix(module:select): fix group label search

[vthinkxie]

close #5276

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?

[ ] 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

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[ ] No

Other information

[zorro-bot]

This preview will be available after the AzureCI is passed.

[codecov]

Codecov Report

Merging #5407 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #5407   +/-   ##
=======================================
  Coverage   91.33%   91.34%           
=======================================
  Files         551      551           
  Lines       13949    13950    +1     
  Branches     2110     2111    +1     
=======================================
+ Hits        12741    12742    +1     
  Misses        717      717           
  Partials      491      491           

Impacted Files	Coverage Δ
components/select/select.component.ts	90.17% <100.00%> (+0.03%)	⬆️

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