Fix blocking I/O in the event loop while processing files in a post request

[bdraco]

What do these changes do?

Fix blocking I/O in the event loop while processing files in a post request

It looks like this was introduced in f2dbdf9

Are there changes in behavior for the user?

event loop is not blocked

Is it a substantial burden for the maintainers to support this?

no

Related issue number

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
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  • Please keep alphabetical order, the file is sorted by names.
• Add a new news fragment into the CHANGES/ folder

  • name it <issue_or_pr_num>.<type>.rst (e.g. 588.bugfix.rst)

  • if you don't have an issue number, change it to the pull request
    number after creating the PR

    • .bugfix: A bug fix for something the maintainers deemed an
      improper undesired behavior that got corrected to match
      pre-agreed expectations.
    • .feature: A new behavior, public APIs. That sort of stuff.
    • .deprecation: A declaration of future API removals and breaking
      changes in behavior.
    • .breaking: When something public is removed in a breaking way.
      Could be deprecated in an earlier release.
    • .doc: Notable updates to the documentation structure or build
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    • .packaging: Notes for downstreams about unobvious side effects
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    • .contrib: Stuff that affects the contributor experience. e.g.
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    • .misc: Changes that are hard to assign to any of the above
      categories.

  • Make sure to use full sentences with correct case and punctuation,
    for example:

    Fixed issue with non-ascii contents in doctest text files
    -- by :user:`contributor-gh-handle`.

    Use the past tense or the present tense a non-imperative mood,
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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.56%. Comparing base (add3937) to head (e5b2c9b).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8283      +/-   ##
==========================================
+ Coverage   97.49%   97.56%   +0.06%     
==========================================
  Files         107      107              
  Lines       32987    32990       +3     
  Branches     3853     3853              
==========================================
+ Hits        32162    32187      +25     
+ Misses        606      588      -18     
+ Partials      219      215       -4     

Flag	Coverage Δ
CI-GHA	97.48% <100.00%> (+0.05%)	⬆️
OS-Linux	97.14% <100.00%> (+0.05%)	⬆️
OS-Windows	95.71% <100.00%> (+<0.01%)	⬆️
OS-macOS	96.85% <100.00%> (+<0.01%)	⬆️
Py-3.10.11	95.56% <100.00%> (+<0.01%)	⬆️
Py-3.10.13	96.70% <100.00%> (?)
Py-3.10.14	96.92% <100.00%> (+<0.01%)	⬆️
Py-3.11.8	97.14% <100.00%> (+<0.01%)	⬆️
Py-3.12.2	97.26% <100.00%> (+<0.01%)	⬆️
Py-3.8.10	95.53% <100.00%> (+<0.01%)	⬆️
Py-3.8.18	96.89% <100.00%> (+<0.01%)	⬆️
Py-3.9.13	95.53% <100.00%> (+<0.01%)	⬆️
Py-3.9.18	?
Py-3.9.19	96.92% <100.00%> (+0.03%)	⬆️
Py-pypy7.3.15	96.45% <100.00%> (?)
VM-macos	96.85% <100.00%> (+<0.01%)	⬆️
VM-ubuntu	97.14% <100.00%> (+0.05%)	⬆️
VM-windows	95.71% <100.00%> (+<0.01%)	⬆️

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[bdraco]

Production test on this one is good as well

[patchback]

Backport to 3.9: 💚 backport PR created

✅ Backport PR branch: patchback/backports/3.9/54e13b0a2a2ac52cedaaa3837f9e93de220a423f/pr-8283

Backported as #8293

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback]

Backport to 3.10: 💚 backport PR created

✅ Backport PR branch: patchback/backports/3.10/54e13b0a2a2ac52cedaaa3837f9e93de220a423f/pr-8283

Backported as #8294

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.