Fix: PHP unit tests issue.

[jorgefilipecosta]

Fixes a unit test issue on #46248.

[github-actions]

Flaky tests detected in eea96be.
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/4134069231
📝 Reported issues:

• [Flaky Test] results in two remaining blocks and positions the caret at the end of the second block #39805 in specs/editor/various/block-deletion.test.js
• [Flaky Test] should handle Enter across blocks #39763 in specs/editor/various/multi-block-selection.test.js