Fix missing TinyMCE license files + tests

[sreichel]

(it will fail for v8)

edit: composer-plugin added license-files for TinyMCE v7.x, but not for v8.x (or later). Fixed in v3.1.

[Copilot]

Pull Request Overview

Ensures TinyMCE license files are present and verified by unit tests; bumps composer plugin to pick up related install behaviors.

• Add PHPUnit tests to assert presence of TinyMCE license files in project root and vendor directory.
• Update dependency constraint openmage/composer-plugin from ^3.0 to ^3.1.

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 2 comments.

File	Description
tests/unit/Base/TinyMCELicenseTest.php	Adds tests that check for TinyMCE license files; uses Composer InstalledVersions to gate tests.
composer.json	Bumps openmage/composer-plugin to ^3.1.

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud