Error with Python 3.8 and older

Python 3.6, 3.7 and 3.8 are currently still supported according to setup.cfg. But when using them this error occurs:

File "vre-middleware/src/virtmat/middleware/resconfig/resconfig.py", line 120, in QueueConfig
    resources: list[ResourceConfig] = field(default_factory=list)
TypeError: 'type' object is not subscriptable

The simple solution is to not support python < 3.9 and keep the code unchanged. Otherwise the module resconfig.py needs a conditional import:

from __future__ import annotations