[ticket/11465] Add tests for optional arguments of get_module_infos()

The possibilities of the first argument have already been covered
previously. The second argument will be covered with an entry that
should exist, an incorrect entry, and the default false entry that
should use the previously set module class. Unfortunately, the third
argument doesn't have an effect in the tests, as the mocked extension
manager will not properly handle enabled/disabled extensions.

PHPBB3-11465