Fix a typo in 5.0 RC release notes (#4638)

[ti-srebot]

cherry-pick #4638 to release-5.0
You can switch your code base to this Pull Request by using git-extras:

# In docs repo:
git pr https://github.com/pingcap/docs/pull/4640

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

git push git@github.com:ti-srebot/docs.git pr/4640:release-5.0-8e0b398e87ad

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What is changed, added or deleted? (Required)

Which TiDB version(s) do your changes apply to? (Required)

• master (the latest development version)
• v5.0 (TiDB 5.0 versions)
• v4.0 (TiDB 4.0 versions)
• v3.1 (TiDB 3.1 versions)
• v3.0 (TiDB 3.0 versions)
• v2.1 (TiDB 2.1 versions)

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

• This PR is translated from: Fix a typo in 5.0 RC release notes docs-cn#5310
• 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