N°3091 Update PHPUnit to 8.5 : fix setUp and teardDown methods signatures

"Return type declaration must be compatible with parent"
See https://phpunit.de/announcements/phpunit-8.html "Return Type of Template Methods"

test/setup/SetupUtilsTest.php

@@ -17,7 +17,7 @@ use SetupUtils;
  */
 class SetupUtilsTest extends ItopTestCase
 {
-	protected function setUp()
+	protected function setUp(): void
 	{
 		parent::setUp();