PaletteEdit: Fix another flaky test

[tyxla]

What?

Fixes another flaky PaletteEdit test. Follow-up to #61791.

Why?

Because it's flaky. Example:
https://github.com/WordPress/gutenberg/actions/runs/9171026029/job/25214476473?pr=61813#step:6:200

How?

We're now explicitly waiting for the "Reset colors" button to appear.

Testing Instructions

All tests should pass. Make sure to do multiple runs of this one to ensure it's no longer flaky:

npm run test:unit:watch packages/components/src/palette-edit/test/index.tsx

Testing Instructions for Keyboard

None

Screenshots or screencast

None

[github-actions]

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Co-authored-by: tyxla <tyxla@git.wordpress.org>
Co-authored-by: cbravobernal <cbravobernal@git.wordpress.org>
Co-authored-by: Mamaduka <mamaduka@git.wordpress.org>

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[cbravobernal]

LGTM

[Mamaduka]

Thank you, @tyxla!

[tyxla]

Thank you both 🙌

[github-actions]

Flaky tests detected in 4678b86.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/9173168284
📝 Reported issues:

• [Flaky Test] Clicking on inserter while on zoom-out should open the patterns tab on the inserter #61806 in /test/e2e/specs/site-editor/zoom-out.spec.js