mirrir -> mirror (#5292)

[ti-srebot]

cherry-pick #5292 to master
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# In docs repo:
git pr https://github.com/pingcap/docs/pull/5295

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git push git@github.com:ti-srebot/docs.git pr/5295:master-d1bb28468409

---

Fixed typo "mirrir" -> "mirror"

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[ti-srebot]

@kolbe please accept the invitation then you can push to the cherry-pick pull requests.
https://github.com/ti-srebot/docs/invitations

[TomShawn]

/label require-LGT1
/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• TomShawn

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[TomShawn]

/merge

[ti-chi-bot]

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

Commit hash: 40f4238