fix(module:dropdown): fix dropdown break SSR

[vthinkxie]

close #5186

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]

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[codecov]

Codecov Report

Merging #5244 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #5244   +/-   ##
=======================================
  Coverage   91.44%   91.44%           
=======================================
  Files         548      548           
  Lines       13859    13864    +5     
  Branches     2091     2091           
=======================================
+ Hits        12673    12678    +5     
  Misses        705      705           
  Partials      481      481           

Impacted Files	Coverage Δ
components/dropdown/dropdown.module.ts	100.00% <ø> (ø)
components/dropdown/dropdown.directive.ts	88.17% <100.00%> (+0.67%)	⬆️
components/timeline/timeline-item.component.ts	100.00% <100.00%> (ø)
components/timeline/timeline.component.ts	97.67% <100.00%> (ø)
components/timeline/timeline.service.ts	100.00% <100.00%> (ø)

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