Recent fix to orjson serialization breaks unions

• cattrs version: 22.1.0.dev0
• Python version: 3.7
• Operating System: Ubuntu 16.04

Description

Orjson doesn't like it when classes have union types as entries. It doesn't always happen, but it does in the case I'm actually working on.

What I Did

Unfortunately, I've been unable to come up with a small example for this one, but I can explain the error:

in orjson.py, there is the section:

        if args:
            if (issubclass(args[0], str) and issubclass(args[0], Enum)):

                def key_handler(v):
                    return v.value

I have managed to get args[0] to be a typing.Union type, which means that this crashes, since issubclass only works on type objects, and typing.Union is not a type object.

This can be fixed by changing it to

        if args:
            if (isinstance(args[0], type) and
                issubclass(args[0], str) and
                issubclass(args[0], Enum)):

                def key_handler(v):
                    return v.value

I suspect this might be the case in other converters as well, but since I'm using orjson, that's the one I ran into it in

Start in orjson.py at the key_handler setup where args[0] is checked with issubclass. Exercise the converter with a class containing a typing.Union entry, then verify that union types no longer trigger the issubclass failure while the existing string Enum handling still works.