Search: fix Tracks value that is causing event to be rejected

[IanRamosC]

Context: pbmo2S-2Eb-p2#comment-3225

Proposed changes:

• This PR fixes a Tracks event that was trying to store a JSON-encoded string as value, but it was causing the event to be rejected (since it doesn't match the allowed pattern)

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
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Jetpack product discussion

pbmo2S-2Eb-p2#comment-3225

Does this pull request change what data or activity we track or use?

No

Testing instructions:

N/a

[github-actions]

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[github-actions]

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[aaronyan]

LGTM! Consider adding a new Tracks event in the future that maps what settings have been changed. It could be something like:

jetpack_search_customberg_setting_changed with eventprops:

• setting_name: <string>
• setting_value: <string>

which fires for every setting that has been changed.