For #12531: Align Settings -> Private browsing to 72dp keyline

[hkaancaliskan]

cc @brampitoyo

Pull Request checklist

• Tests: This PR includes thorough tests or an explanation of why it does not
• Screenshots: This PR includes screenshots or GIFs of the changes made or an explanation of why it does not
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features. In addition, it includes a screenshot of a successful accessibility scan to ensure no new defects are added to the product.

After merge

• Milestone: Make sure issues finished by this pull request are added to the milestone of the version currently in development.

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[NotWoods]

LGTM!

[brampitoyo]

@hakkikaancaliskan Looks good to me, as well!

[hkaancaliskan]

@NotWoods could you please label this as needs landing?

[person808]

Closing for #12654