feat(module: carousel): update testing coverage

[Guoyuanqiang]

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-mobile/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

[codecov]

Codecov Report

Merging #511 into master will increase coverage by 0.14%.
The diff coverage is 86.2%.

@@            Coverage Diff             @@
##           master     #511      +/-   ##
==========================================
+ Coverage   88.38%   88.52%   +0.14%     
==========================================
  Files         269      269              
  Lines        7514     7514              
  Branches     1064     1064              
==========================================
+ Hits         6641     6652      +11     
+ Misses        455      439      -16     
- Partials      418      423       +5

Impacted Files	Coverage Δ
components/carousel/carousel.component.ts	71.42% <86.2%> (+5.1%)	⬆️
components/picker/picker.service.ts	80% <0%> (-5%)	⬇️
components/picker/picker.component.ts	67.5% <0%> (-1.5%)	⬇️

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