EZP-21008: Replaced assertType() with assertInternalType()

The `assertType()` method has been removed in favor of `assertInternalType()`. `assertType()` has been ["silently" deprecated](https://github.com/sebastianbergmann/phpunit/issues/77#issuecomment-619328) in PHPUnit 3.5 and removed in 3.6.

So, the Unit Tests for eZ Comments will continue to work in PHPUnit 3.5 (the minimum version for eZ Publish), but later will fail (which they did when I installed a new eZ Publish Legacy from the git master branch with the demo extension).

This patch changes `assertType()` calls to `assertInternalType()`.

Cheers
:octocat: Jérôme

https://jira.ez.no/browse/EZP-21008