fix(module:switch): fix switch ViewChild static

[vthinkxie]

close #3760

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

[netlify]

Deploy preview for ng-zorro-master ready!

Built with commit 07316ff

https://deploy-preview-3784--ng-zorro-master.netlify.com

[codecov]

Codecov Report

Merging #3784 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #3784   +/-   ##
=======================================
  Coverage   95.39%   95.39%           
=======================================
  Files         712      712           
  Lines       14543    14543           
  Branches     1913     1913           
=======================================
  Hits        13874    13874           
  Misses        243      243           
  Partials      426      426

Impacted Files	Coverage Δ
components/switch/nz-switch.component.ts	98.27% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 4926b32...07316ff. Read the comment docs.