Build/Test Tools: Reference reusable-prepare-gutenberg.yml at trunk in the 7.0 PHPUnit workflow

[lancewillett]

This updates the 7.0 PHPUnit workflow to reference reusable-prepare-gutenberg.yml@trunk instead of a pinned commit SHA.

The reusable-phpunit-tests-v3.yml callers already use @trunk. Keeping both shared workflows on the same ref prevents their output contract from drifting and preserves the one-version-to-maintain intent.

No PHP matrix or caller wiring changed.

Trac ticket: https://core.trac.wordpress.org/ticket/65721

Testing

• actionlint .github/workflows/phpunit-tests.yml
• git diff --check

Use of AI Tools

AI assistance: Yes
Tool(s): Codex
Model(s): GPT-5
Used for: Applied and validated the one-line workflow reference change. The final diff was reviewed by me.

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request.

[Copilot]

Pull request overview

Updates the GitHub Actions 7.0 PHPUnit workflow to track the reusable-prepare-gutenberg.yml reusable workflow on trunk (instead of a pinned commit), aiming to keep the “prepare” producer aligned with other PHPUnit workflow consumers already following @trunk.

Changes:

• Switch prepare-gutenberg to use reusable-prepare-gutenberg.yml@trunk rather than a pinned SHA.
• Add an inline note and a zizmor suppression for the unpinned uses: reference.

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