fix(module:steps): fix steps ngfor

[vthinkxie]

close #1418

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

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[codecov]

Codecov Report

Merging #1421 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1421      +/-   ##
==========================================
+ Coverage   96.94%   96.96%   +0.02%     
==========================================
  Files         196      196              
  Lines        8370     8370              
  Branches     1106     1106              
==========================================
+ Hits         8114     8116       +2     
+ Misses         36       35       -1     
+ Partials      220      219       -1

Impacted Files	Coverage Δ
components/steps/nz-steps.component.ts	96.72% <100%> (ø)	⬆️
components/table/nz-table.component.ts	95.48% <0%> (+1.29%)	⬆️

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