fix(module:tree-select): should be not clearable when disabled or unselected

[hsuanxyz]

close #5603

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: #5603

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[codecov]

Codecov Report

Merging #5769 into master will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5769      +/-   ##
==========================================
- Coverage   90.07%   90.07%   -0.01%     
==========================================
  Files         455      455              
  Lines       13856    13862       +6     
  Branches     2267     2269       +2     
==========================================
+ Hits        12481    12486       +5     
- Misses        848      849       +1     
  Partials      527      527              

Impacted Files	Coverage Δ
components/tree-select/tree-select.component.ts	93.46% <ø> (ø)
components/carousel/strategies/base-strategy.ts	83.33% <0.00%> (-7.58%)	⬇️
...mponents/carousel/strategies/transform-strategy.ts	89.88% <0.00%> (ø)
components/carousel/carousel.component.ts	93.70% <0.00%> (+1.29%)	⬆️

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[github-actions]

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