Add v0.21 to NLPModels compatibility

[MaxenceGollier]

I often need it when I want to use CUTEst with versions later than 1.0 (which I need for using it on Windows).
I see no reason for not having it.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.36%. Comparing base (e0f214d) to head (76ff123).
Report is 89 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #197      +/-   ##
==========================================
- Coverage   61.53%   59.36%   -2.17%     
==========================================
  Files          11       15       +4     
  Lines        1292     1885     +593     
==========================================
+ Hits          795     1119     +324     
- Misses        497      766     +269     

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[github-actions]

Here are the
demos-results

[dpo]

Thank you.