Add failing unit test related to DBAL-1063

I am not 100% sure, but I think the behavior exposed by this test is one of the factors in DBAL-1063. But even if it wasn't, it is still very confusing that `Table::getIndexes` doesn't return the same thing as `SchemaManager::listTableIndexes` when they are both called on the same table.

I've written the test against the MySQL SM, but I suspect the same might happen with other platforms as well