Fix typo – "muti-author" to "multi-author"

[mokagio]

I noticed this while reading the encrypted logs in one of the tickets I worked on during my yearly support rotation.

Regression Notes

1. Potential unintended areas of impact – N.A.
2. What I did to test those areas of impact (or what existing automated tests I relied on) – N.A.
3. What automated tests I added (or what prevented me from doing so) – N.A.

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• I have completed the Regression Notes.
• I have considered adding unit tests for my changes. N.A.
• I have considered adding accessibility improvements for my changes. N.A.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary. N.A.

[peril-wordpress-mobile]

	Warnings
⚠️	PR is not assigned to a milestone.
⚠️	PR is missing at least one label.

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[wpmobilebot]

You can test the changes in WordPress from this Pull Request by:

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[wpmobilebot]

You can test the changes in Jetpack from this Pull Request by:

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• Then installing the build number pr19897-0d41204 on your iPhone

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[derekblank]

LGTM! 👀 🚀