Fix server error from DAB ValidationError with strings

[AlanCoding]

SUMMARY

Took me a while to process, msg_data is not what gets used in the response. It is only used for a log message. This threw errors when DAB code raise ValidationError('foo'), because of a baked-in assumption that when it gets a list (this is converted to a list of element 1) it is a list of dictionaries.

I'm not defending the specific error formatting in these cases, but that's a different subject. This fixes the server error that comes from logic to build a log message that doesn't even go in the response. However we format the error, we should not return a 500.

AAP-25540

MORE CONTEXT:

This is happening because we have a DAB view (role user assignment list) which re-parents itself under the main AWX generic API view. It's weird. This allows DAB views to inherit request finalization logic (like this) but also can expose corner cases from assumptions that were always true in AWX but not always true generally.

ISSUE TYPE

• Bug, Docs Fix or other nominal change

COMPONENT NAME

• API