fix(module:cron-expression): output type error

[OriginRing]

fix: #8188

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
[ ] No

Other information

[zorro-bot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (e75de2b) 91.70% compared to head (a269820) 91.71%.
Report is 5 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #8189   +/-   ##
=======================================
  Coverage   91.70%   91.71%           
=======================================
  Files         519      519           
  Lines       17885    17890    +5     
  Branches     2747     2836   +89     
=======================================
+ Hits        16402    16407    +5     
  Misses       1181     1181           
  Partials      302      302           

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[HyperLife1119]

LGTM