[Docs] Fix typo in hook document

[acdart]

Motivation

fix type error in custom_hooks doc.

Modification

update en and zh_cn hooks doc.

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.

[CLAassistant]

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[HAOCHENYE]

@acdart Hi! Thanks for your contribution! please sign the CLA first.