[issue30098] Verbose TypeError for asyncio.ensure_future

[crenwick]

crenwick added the comment:

Totally understandable. Some final thoughts:

> this is the first time I see somebody tries to use `ensure_future` on `run_coroutine_threadsafe` result, which suggests that it's not a common problem.

 - I wonder how much self-reporting will be done here.

 - I also considered making the existing error message more verbose (I think that still could be effective). However, I decided to open this PR as a separate TypeError to not muddle the language of the probably more common TypeError.

Thanks for your time and insight, Yury!

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