Backport 6a6ab7d and c5d399 to 3.1

[pfreixes]

What do these changes do?

Backports the fix related to the #2909 issue for the 3.1 branch.

Note that due that fix was finally made using two commits the backport has been by hand but trying to keep the nomenclature imposed by cherry_picker /cc @Mariatta

[codecov-io]

Codecov Report

Merging #2915 into 3.1 will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              3.1    #2915      +/-   ##
==========================================
+ Coverage   97.98%   97.98%   +<.01%     
==========================================
  Files          39       39              
  Lines        7499     7501       +2     
  Branches     1316     1317       +1     
==========================================
+ Hits         7348     7350       +2     
  Misses         48       48              
  Partials      103      103

Impacted Files	Coverage Δ
aiohttp/http_writer.py	100% <100%> (ø)	⬆️

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[pfreixes]

Releases are automatic?

[asvetlov]

No, I should do it. Please wait for a while

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a [new issue] for related bugs.
If you feel like there's important points made in this discussion, please include those exceprts into that [new issue].
[new issue]: https://github.com/aio-libs/aiohttp/issues/new