Fix web.FileResponse overriding user supplied Content-Type

[thelink2012]

What do these changes do?

If the user modifies either the web.FileResponse.content_type property, or the Content-Type header, the choice is now respected instead of guessing the content type from the file extension.

Are there changes in behavior for the user?

No notable changes should happen.

Related issue number

Fixes #2317

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes (no need I guess)
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
• Add a new news fragment into the changes folder

[codecov-io]

Codecov Report

Merging #2319 into 2.2 will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              2.2    #2319      +/-   ##
==========================================
+ Coverage   97.06%   97.06%   +<.01%     
==========================================
  Files          38       38              
  Lines        7691     7694       +3     
  Branches     1341     1342       +1     
==========================================
+ Hits         7465     7468       +3     
  Misses        102      102              
  Partials      124      124

Impacted Files	Coverage Δ
aiohttp/web_fileresponse.py	90.72% <100%> (+0.18%)	⬆️

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[asvetlov]

Thanks!

[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