Restore PHPUnit CI on Ubuntu 24.04

[ashfame]

Summary

• Install Subversion explicitly before setting up the WordPress PHPUnit test suite.
• Skip transformed-post cleanup when no transformed post was created.
• Keep the workflow on ubuntu-latest instead of pinning it to the deprecated Ubuntu 22.04 image.

Root cause

The WordPress test installer uses svn export, but ubuntu-latest now resolves to Ubuntu 24.04, whose hosted-runner image deliberately omits Subversion. This caused PR 197's PHPUnit job to fail before tests with svn: command not found. The runner-images maintainers confirmed the Ubuntu 22.04 to 24.04 regression and recommend installing the package in the workflow: actions/runner-images#11219.

Once the test bootstrap ran again, WordPress 6.9+'s validation exposed an existing teardown call to wp_delete_post(0). The cleanup now calls wp_delete_post() only when a transformed post exists.

Validation

• Ran actionlint; the changed workflow introduces no new diagnostics (the existing numeric service-port access warning remains).
• Installed Subversion 1.14.3 with the proposed command in an Ubuntu 24.04 container.
• Successfully exported the same WordPress 7.0.2 PHPUnit files used by the CI bootstrap.
• Ran PHP syntax validation and the repository's Composer lint script.
• GitHub Actions passes PHPUnit 8.3 (46 tests), PHP linting, and browser-extension linting.

[Copilot]

Pull request overview

This PR updates the PHPUnit GitHub Actions workflow to keep running on ubuntu-latest (Ubuntu 24.04) while ensuring the WordPress PHPUnit bootstrap can run successfully by installing Subversion (required for svn export).

Changes:

• Adds an explicit “Install Subversion” step (apt-get install subversion) before the WordPress test setup step.
• Retains runs-on: ubuntu-latest rather than pinning to Ubuntu 22.04.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.