correct version info for v5.0

[TomShawn]

What is changed, added or deleted? (Required)

Correct version information in system-variables.md

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:
• Other reference link(s): update async commit related documentations (#5607) #5812

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

[TomShawn]

/status PTAL
/size small
/translation doing
/cc @qiancai @CharLotteiu

[TomShawn]

/assign

[qiancai]

/lgtm

[ti-chi-bot]

@qiancai: /lgtm is only allowed for the reviewers in list.

Details

In response to this:

/lgtm

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[CharLotteiu]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• CharLotteiu

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

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Details

Reviewer can indicate their review by writing /lgtm in a comment.
Reviewer can cancel approval by writing /lgtm cancel in a comment.

[TomShawn]

/merge

[ti-chi-bot]

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

Details

Commit hash: c7dee08

[TomShawn]

/remove-translation doing
/translation done