Fix handling of value when multiple files in form-data

It appears that the value list extracted from the `FormData`
is not necessarily composed of `UploadFile` instances.

fastapi/dependencies/utils.py

@@ -778,7 +778,10 @@ async def request_body_to_args(
 
                 async with anyio.create_task_group() as tg:
                     for sub_value in value:
-                        tg.start_soon(process_fn, sub_value.read)
+                        if isinstance(sub_value, UploadFile):
+                            tg.start_soon(process_fn, sub_value.read)
+                        else:
+                            results.append(sub_value)
                 value = sequence_shape_to_type[field.shape](results)
 
             v_, errors_ = field.validate(value, values, loc=loc)