EZP-21432: Fixed wrong assertions

Unfortunately, in PR #30, I have introduced two assertion errors in [https://github.com/ezsystems/ezcomments/commit/2cdf323bcf514cd5dd59100e5894865028bdf5b1#L1L45](ackages/ezcomments_extension/ezextension/ezcomments/tests/ezcomnotification_test.php)

`$this->assertInstanceOf( 'ezcomComment', $notification );`

should be

`$this->assertType( 'ezcomNotification', $notification );`