[3.7] Better checksum calculation (#5183)

[github-actions]

Backports the following commits to 3.7:

• Better checksum calculation (Better checksum calculation #5183)

[codecov-io]

Codecov Report

Merging #5185 into 3.7 will increase coverage by 0.09%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##              3.7    #5185      +/-   ##
==========================================
+ Coverage   97.45%   97.55%   +0.09%     
==========================================
  Files          44       44              
  Lines        8818     8818              
  Branches     1419     1419              
==========================================
+ Hits         8594     8602       +8     
+ Misses        109      101       -8     
  Partials      115      115              

Flag	Coverage Δ
unit	97.55% <ø> (+0.09%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
aiohttp/helpers.py	95.89% <0.00%> (ø)
aiohttp/http_websocket.py	98.67% <0.00%> (+0.26%)	⬆️
aiohttp/http_parser.py	97.51% <0.00%> (+0.90%)	⬆️
aiohttp/http_writer.py	98.16% <0.00%> (+0.91%)	⬆️
aiohttp/frozenlist.py	100.00% <0.00%> (+4.16%)	⬆️

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