text: Title: Using type() to compare types - cannot use class that has `str` as base class
  Body: It's not possible to use `StrEnum(str, Enum)` object as a key because of following code: https://github.com/aio-libs/aioredis/blob/231d0418988fd870c3d26d60eec65e2fc13d0144/aioredis/util.py#L35
  
  Unfortunately this code requires argument to by strictly `str` type instead of being a subclass of `str`.
  
  What I'd like to achieve is following:
  
  ```python
  from enum import Enum
  
  class StrEnum(str, Enum):
       AAA = "aaa"
  
  # ....
  
  rdb.hmget("key", StrEnum.AAA)
  ```
        