QueueManager Fails when Multiple Queue Configs Contain uniqueCache Key #113

When multiple queue configs have the uniqueCache key QueueManager fails to load with the following error:

BadMethodCallException: Cannot reconfigure existing key "Cake/Queue.queueUnique"

/code/vendor/cakephp/cakephp/src/Core/StaticConfigTrait.php:91
/code/src/QueueManager.php:130

The following test can be used to trigger the error:

public function testMultipleUniqueCache()
{
    QueueManager::setConfig('test', [
        'url' => 'null:',
        'uniqueCache' => [
            'engine' => 'File',
        ],
    ]);
    QueueManager::setConfig('test2', [
        'url' => 'null:',
        'uniqueCache' => [
            'engine' => 'File',
        ],
    ]);
}