N°4624 Restore processIsolation on tests which actually need it

Warning, one symptom was having the CI returning an empty phpunit.results.xml !!

test/postbuild_integration/iTopDesignFormatChecklistTest.php

@@ -12,6 +12,8 @@ use PHPUnit\Exception;
  * Ticket 3053 - Check XML conversion methods
  *
  * @covers iTopDesignFormat
+ *
+ * @package Combodo\iTop\Test\UnitTest\Setup
  */
 class TestForITopDesignFormatClass extends ItopTestCase
 {