fix(module:descriptions): fix dom structure under vertical layout

[stygian-desolator]

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: N/A

close #6512

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[zorro-bot]

This preview will be available after the AzureCI is passed.

[codecov]

Codecov Report

Merging #6513 (d24e5bd) into master (c2f44be) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #6513   +/-   ##
=======================================
  Coverage   89.86%   89.86%           
=======================================
  Files         479      479           
  Lines       15323    15323           
  Branches     2333     2333           
=======================================
  Hits        13770    13770           
  Misses        935      935           
  Partials      618      618           

Impacted Files	Coverage Δ
components/descriptions/descriptions.component.ts	100.00% <ø> (ø)
components/tabs/tab-nav-bar.component.ts	83.09% <0.00%> (ø)

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[wzhudev]

LGTM. Thank you.