mysql-compatibility.md: Add note about JOIN on subquery

[hfxsd]

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• This PR is translated from:mysql-compatibility.md: Add note about JOIN on subquery docs#20309
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[hfxsd]

/approve

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #19885.
But this PR has conflicts, please resolve them!

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #19886.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #19887.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #19888.