Fix doc build on docs.rs

[syl20bnr]

Should fix #1141

Unfortunately I was not able to test it properly because the docs.rs documentation is very sparse and I encountered several obstacles (even in an Ubuntu VM). I'll try to make it work before the release if I can get good support on zulip.

While I cannot guarantee that it will fix the issue, a local cargo doc seems to skip the torch-sys build with these added metadata (even if the name is related to docs.rs). So high chance we will be good 🙂

Checklist

• Confirmed that run-checks all script has been executed.
• Made sure the book is up to date with changes in this PR.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (c9cc132) 86.01% compared to head (c64f960) 86.01%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1168      +/-   ##
==========================================
- Coverage   86.01%   86.01%   -0.01%     
==========================================
  Files         522      522              
  Lines       58674    58674              
==========================================
- Hits        50469    50466       -3     
- Misses       8205     8208       +3     

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[nathanielsimard]

I remember that it was needed when including this backend in the doc. So I think this will work.