Finish PR 734 : typo in \text{max_nz} in ot.utils.projection_sparse_simplex

[rflamary]

Types of changes

This is a version of PR #734 with release file completed and doc updated

Motivation and context / Related issue

How has this been tested (if it applies)

PR checklist

• I have read the CONTRIBUTING document.
• The documentation is up-to-date with the changes I made (check build artifacts).
• All tests passed, and additional code has been covered with new tests.
• I have added the PR and Issue fix to the RELEASES.md file.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.10%. Comparing base (a97a788) to head (4691a17).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #746   +/-   ##
=======================================
  Coverage   97.10%   97.10%           
=======================================
  Files         100      100           
  Lines       20453    20453           
=======================================
  Hits        19861    19861           
  Misses        592      592           

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