PaletteEdit: Fix flaky test

[tyxla]

What?

Fixes a flaky PaletteEdit test

Why?

Because it's flaky. Example:

• https://github.com/WordPress/gutenberg/actions/runs/9158832871/job/25178298698?pr=61789

How?

We're now explicitly waiting for the "Remove all 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>

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[cbravobernal]

Tested 10 runs.
Without: 1/5 failed.
With: 0/5 failed.

[github-actions]

Flaky tests detected in 6ce2cdf.
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/9159075288
📝 Reported issues:

• [Flaky Test] Items list is reachable via TAB #61701 in /test/e2e/specs/site-editor/dataviews-list-layout-keyboard.spec.js

[Mamaduka]

Unfortunately, this doesn't seem to have resolved the issue - https://github.com/WordPress/gutenberg/actions/runs/9171026029/job/25214476473?pr=61813#step:6:200.

[tyxla]

Unfortunately, this doesn't seem to have resolved the issue - https://github.com/WordPress/gutenberg/actions/runs/9171026029/job/25214476473?pr=61813#step:6:200.

This one seems to be a different one. Fix suggested in #61818.