activate W293 and E714 in pyx files

[fchapoton]

📚 Description

This fixes and activate the pycodestyle warnings

W293: blank line contains whitespace

and

E714: Test for object identity should be 'is not'

in all .pyx files inside src/sage

📝 Checklist

• I have made sure that the title is self-explanatory and the description concisely explains the PR.
• I have linked an issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation accordingly.

⌛ Dependencies

[dcoudert]

LGTM.

[fchapoton]

Merci David. Faut approuver, je crois, pour que ça soit fusionné.

[dcoudert]

I agree with these changes

[vbraun]

merge conflict

[codecov-commenter]

Codecov Report

Patch coverage has no change and project coverage change: -0.03 ⚠️

Comparison is base (c00e6c2) 88.62% compared to head (fe1e890) 88.60%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #35165      +/-   ##
===========================================
- Coverage    88.62%   88.60%   -0.03%     
===========================================
  Files         2148     2148              
  Lines       398855   398855              
===========================================
- Hits        353480   353396      -84     
- Misses       45375    45459      +84     

see 31 files with indirect coverage changes

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[github-actions]

Documentation preview for this PR is ready! 🎉
Built with commit: fe1e890

[fchapoton]

setting back to positive after trivial merge

[dcoudert]

Was about to do it. LGTM.