fix(module: radio-item-group): fix checked error. (#458)

[Anberm]

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-mobile/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: #458

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[codecov]

Codecov Report

Merging #463 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #463      +/-   ##
==========================================
+ Coverage   85.57%   85.58%   +<.01%     
==========================================
  Files         270      270              
  Lines        7597     7601       +4     
  Branches     1087     1087              
==========================================
+ Hits         6501     6505       +4     
  Misses        671      671              
  Partials      425      425

Impacted Files	Coverage Δ
components/radio/radio-item.component.ts	93.75% <100%> (+0.41%)	⬆️
components/radio/radio-item-group.component.ts	81.39% <100%> (+0.9%)	⬆️

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