Notes: Fix flaky thread scroll e2e test

[Mamaduka]

What?

Noticed in #84101 and #84110

Adds spacer paragraphs below the noted block in the "scrolls the thread before the canvas" e2e test. The test was flaky on CI: its last assertion failed with Expected: > 221, Received: 221.

Why?

The post held only the noted paragraph, so the canvas could scroll at most 221px. After the replies were added, the canvas started anywhere from 204 to 221. When it started at 221, it was already at the bottom, so a wheel scroll past the end of the thread could not move it.

Testing Instructions

1. Run npm run test:e2e -- test/e2e/specs/editor/various/block-notes-floating.spec.js -g "scrolls the thread before the canvas" --repeat-each=20 --retries=0.
2. All runs pass.

Before the fix, 2 of 10 local Chromium runs failed at the canvas assertion. After the fix, 20 of 20 passed. The full block-notes-floating.spec.js suite passes (34 tests).

Use of AI Tools

Claude Code found the cause, wrote the fix and ran the tests. I reviewed the change.

[github-actions]

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

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📦 Bundle size

Size Change: 0 B

Total Size: 8.29 MB

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[adamsilverstein]

Good!