Fix a typo in Update character-set-and-collation.md (#6124)

[ti-srebot]

cherry-pick #6124 to release-3.0
You can switch your code base to this Pull Request by using git-extras:

# In docs-cn repo:
git pr https://github.com/pingcap/docs-cn/pull/6126

After apply modifications, you can push your change to this PR via:

git push [email protected]:ti-srebot/docs-cn.git pr/6126:release-3.0-41d6eac66286

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What is the related PR or file link(s)?

Fix a typo in Update character-set-and-collation.md

• This PR is translated from: Fix a typo in Update character-set-and-collation.md docs#5448
• Other reference link(s):

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[ti-srebot]

@Joyinqin you're already a collaborator in bot's repo.

[TomShawn]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• TomShawn

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[TomShawn]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 365e747