Moved common data provider for core unit tests to trait

module/Core/test/Util/ApiKeyHelpersTrait.php

@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+namespace ShlinkioTest\Shlink\Core\Util;
+
+use Shlinkio\Shlink\Rest\Entity\ApiKey;
+
+trait ApiKeyHelpersTrait
+{
+    public function provideAdminApiKeys(): iterable
+    {
+        yield 'no API key' => [null];
+        yield 'admin API key' => [new ApiKey()];
+    }
+}