Interactivity API: Fix flaky test on-window, remove duplicate expect on-document.

[cbravobernal]

What?

Fixes #57983

Removes duplicate assertion spotted in #58008 (comment)

[github-actions]

Flaky tests detected in 197ab8f.
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/7640577286
📝 Reported issues:

• [Flaky Test] Only the first block is an empty paragraph block #58161 in /test/e2e/specs/editor/blocks/paragraph.spec.js

[github-actions]

Warning: Type of PR label mismatch

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• Labels found: [Type] Flaky Test, [Feature] Interactivity API, [Packages] Interactivity.

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[luisherranz]

LGTM. Let's see if this time it's for real 😄