fix a spell error in docs/zh_cn

[cxiang26]

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Motivation

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Modification

也可以在定义类是给定优先级
是 -> 时

BC-breaking (Optional)

Does the modification introduce changes that break the backward-compatibility of the downstream repos?
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Use cases (Optional)

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Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDet or MMCls.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[HAOCHENYE]

Hi, thanks for your contribution, it seems you should update your code with the latest main branch.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (dev@3ba50ce). Click here to learn what that means.
Patch has no changes to coverable lines.

Additional details and impacted files

@@          Coverage Diff           @@
##             dev     #548   +/-   ##
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  Coverage       ?   77.66%           
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  Files          ?      116           
  Lines          ?     8644           
  Branches       ?     1787           
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  Hits           ?     6713           
  Misses         ?     1631           
  Partials       ?      300           

Flag	Coverage Δ
unittests	77.66% <0.00%> (?)

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