Fix Thold integration dependency installation

[somethingwithproof]

Summary

• remove the unavailable Ubuntu-versioned Apache PHP package from the integration matrix

The matrix PHP executable is supplied by setup-php; the integration suite runs through the CLI and does not require an Apache module.

Validation

• git diff --check
• workflow YAML parsed successfully

Kept separate from #773 so the security hardening remains focused.

[Copilot]

Pull request overview

This PR updates the GitHub Actions integration-test workflow to avoid installing an Ubuntu-versioned Apache PHP module that is not reliably available across the PHP matrix, relying instead on setup-php for the CLI PHP runtime.

Changes:

• Removed libapache2-mod-php${{ matrix.php }} from the system dependency installation step in the integration workflow.

[somethingwithproof]

Re-verified: branch is up to date with develop (no rebase needed), all 4 Integration Test checks currently pass. One Copilot thread on plugin-ci-workflow.yml:90 (about /usr/bin/php not existing after removing the apt package) is marked outdated — the concern looks already addressed by this PR's own $PHP_BINARY capture/usage further down the diff, so leaving it as-is. No changes pushed.