Cleanup no longer necessary assert

Author: staabm

src/TextUI/Output/TestDox/ResultPrinter.php

@@ -209,8 +209,6 @@ private function printTestResultBodyEnd(TestDoxTestResult $test): void
 
     private function printThrowable(TestStatus $status, Throwable $throwable): void
     {
-        assert($throwable instanceof Throwable);
-
         $message    = trim($throwable->description());
         $stackTrace = $this->formatStackTrace($throwable->stackTrace());
         $diff       = '';