Changelog:
==========
- Fixed "Unclosed client session" when initialization of
:py:class:~aiohttp.ClientSession fails -- by :user:NewGlad.
- Fixed regression (from :pr:8280) with adding Content-Disposition to the form-data
part after appending to writer -- by :user:Dreamsorcerer/:user:Olegt0rr.
- Added default Content-Disposition in multipart/form-data responses to avoid broken
form-data responses -- by :user:Dreamsorcerer.
Signed-off-by: Wang Mingyu <wangmy@fujitsu.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>
