Issue #3546496: Declare 'user' and 'node' module dependencies in PluginTestBase

Closes #3546496

Issue

PluginTestBase was using plugins that reference the user and node entity types without declaring the required modules as dependencies. This caused kernel tests to fail with: Drupal\Component\Plugin\Exception\PluginNotFoundException: The "user" entity type does not exist.

Fix

• Added 'user' and 'node' to the $modules array in PluginTestBase.
• Ensures that the required entity types are available during kernel tests.
• Verified that all plugin kernel tests pass after this change.

Code Change

protected static $modules = [
    'plugin_test',
    'user',
    'node',
];