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/core/WeeklyScheduledProcessTest.php

@@ -7,7 +7,7 @@ use DateTime;
 
 class WeeklyScheduledProcessTest extends ItopTestCase
 {
-	protected function setUp()
+	protected function setUp(): void
 	{
 		parent::setUp();
 		require_once(APPROOT.'core/backgroundprocess.inc.php');