post_migrate expects too many arguments

According to https://edugit.org/AlekSIS/official/AlekSIS-Core/-/blob/master/aleksis/core/apps.py#L104, post_migrate needs six positional arguments. This causes problems as there are Django parts that call the signal with just four positional arguments (https://github.com/django/django/blob/23fa29f6a6659e0f600d216de6bcb79e7f6818c9/django/core/management/sql.py#L46) and even without the last two positional arguments as keyword arguments (https://github.com/django/django/blob/main/django/core/management/commands/flush.py#L80).

So, I think we should remove plan and apps as explicit positional arguments and include them in kwargs.