fix(module:select): fix select search display

[vthinkxie]

close #3322

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

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[codecov]

Codecov Report

Merging #3324 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #3324   +/-   ##
=======================================
  Coverage   97.44%   97.44%           
=======================================
  Files         606      606           
  Lines       11930    11930           
  Branches      869      869           
=======================================
  Hits        11625    11625           
  Misses        196      196           
  Partials      109      109

Impacted Files	Coverage Δ
...mponents/select/nz-select-top-control.component.ts	100% <100%> (ø)	⬆️

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