Fix phpstan tests for PHP 7.2+

Author: tomas-novotny

Diff for: tests/AbstractTestCase.php

@@ -13,7 +13,7 @@ abstract class AbstractTestCase extends PHPUnitTestCase
      *
      * @return void
      */
-    protected function setUp()
+    protected function setUp(): void
     {
         parent::setUp();
 
@@ -25,7 +25,7 @@ protected function setUp()
      *
      * @return void
      */
-    protected function tearDown()
+    protected function tearDown(): void
     {
         parent::tearDown();