Revert: wp_mock to 0.3.0 and remove :void from AdminTest::setUp

tests/test-admin.php

@@ -30,7 +30,7 @@ class AdminTest extends \WP_Mock\Tools\TestCase {
     /**
      * Set up test environment
      */
-    public function setUp(): void {
+    public function setUp() {
         parent::setUp();
 
         // Set up mocks