🌐 Add French translation for docs/async.md

[Smlep]

Hey everyone!

Here is the PR to translate the async await doc page section into french.
See the french translation tracking issue here.

Thanks for the reviews👌

[codecov]

Codecov Report

Merging #3416 (3941130) into master (0a84d48) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff             @@
##            master     #3416    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files          248       254     +6     
  Lines         7712      7860   +148     
==========================================
+ Hits          7712      7860   +148     

Impacted Files	Coverage Δ
fastapi/routing.py	100.00% <0.00%> (ø)
fastapi/openapi/utils.py	100.00% <0.00%> (ø)
fastapi/openapi/models.py	100.00% <0.00%> (ø)
tests/test_tutorial/test_body/test_tutorial001.py	100.00% <0.00%> (ø)
..._tutorial/test_custom_response/test_tutorial006.py	100.00% <0.00%> (ø)
...tutorial/test_custom_response/test_tutorial006b.py	100.00% <0.00%> (ø)
...tutorial/test_custom_response/test_tutorial006c.py	100.00% <0.00%> (ø)
...tutorial/test_custom_response/test_tutorial009b.py	100.00% <0.00%> (ø)
tests/test_custom_schema_fields.py	100.00% <0.00%> (ø)
..._tutorial/test_custom_response/test_tutorial009.py	100.00% <0.00%> (ø)
... and 1 more

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[github-actions]

📝 Docs preview for commit 1ca7b8d at: https://60df27b73a6af3f689aa1442--fastapi.netlify.app

[github-actions]

📝 Docs preview for commit 0d19780 at: https://60df39033a6af30c23aa10ea--fastapi.netlify.app

[Cajuteq]

I left comments on the section that could be better imo. It is great work overall and the suggested changes may not all be relevant.

[github-actions]

📝 Docs preview for commit 3941130 at: https://60f2e18cbf06fe05643565ab--fastapi.netlify.app

[Smlep]

@Cajuteq I've updated the PR according to your suggestions, if everything's fine with you now you can approve the PR.

[tiangolo]

Awesome, thank you @Smlep! 🚀

And thank you for the reviews @Cajuteq and @rjNemo 🙇