fix(module:tree-select): default tags incorrect in strictly mode

[hsuanxyz]

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: #4364

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[netlify]

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[codecov]

Codecov Report

Merging #4368 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4368      +/-   ##
==========================================
- Coverage    92.2%   92.19%   -0.01%     
==========================================
  Files         520      520              
  Lines       11039    11036       -3     
  Branches     1997     1997              
==========================================
- Hits        10178    10175       -3     
  Misses        429      429              
  Partials      432      432

Impacted Files	Coverage Δ
components/tree/nz-tree.component.ts	97.74% <100%> (-0.07%)	⬇️
components/tree-select/nz-tree-select.component.ts	98.93% <100%> (ø)	⬆️
components/core/tree/nz-tree-base.service.ts	93.62% <0%> (-0.4%)	⬇️
components/typography/nz-typography.component.ts	98.97% <0%> (+1.02%)	⬆️

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