Update Fenix initial experiments JSON for Nimbus (backport #1858)

[rocketsroger]

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• Quality: This PR builds and passes detekt/ktlint checks (A pre-push hook is recommended)
• Tests: This PR includes thorough tests or an explanation of why it does not
• Changelog: This PR includes a changelog entry or does not need one
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• Breaking Changes: If this is a breaking Android Components change, please push a draft PR on Reference Browser to address the breaking issues.

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[rocketsroger]

Manual uplift for #1858

[rvandermeulen]

Approved for 113.0rc1.