test(module:button): added missing tests

[ParsaArvanehPA]

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: missing unit tests for the button Component

What is the current behavior?

What is the new behavior?

	Before	After
Statements	100%	100%
Branches	93.33%	100%
Functions	100%	100%
Lines	100%	100%

Does this PR introduce a breaking change?

• [ ] Yes
• [✔] No

Other information

[zorro-bot[bot]]

This preview will be available after the AzureCI is passed.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.94%. Comparing base (ce2aa55) to head (3132815). Report is 42 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #8788 +/- ## ========================================== - Coverage 93.17% 91.94% -1.23% ========================================== Files 538 537 -1 Lines 18457 18457 Branches 2816 2816 ========================================== - Hits 17197 16970 -227 + Misses 1222 1184 -38 - Partials 38 303 +265 ``` | [Flag](https://app.codecov.io/gh/NG-ZORRO/ng-zorro-antd/pull/8788/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NG-ZORRO) | Coverage Δ | | |---|---|---| | [](https://app.codecov.io/gh/NG-ZORRO/ng-zorro-antd/pull/8788/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NG-ZORRO) | `?` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NG-ZORRO#carryforward-flags-in-the-pull-request-comment) to find out more.

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