Bump to NLPModels 0.20

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (c314a0c) 77.63% compared to head (8b302a6) 77.63%.

:exclamation: Current head 8b302a6 differs from pull request most recent head 9f5126b. Consider uploading reports for the commit 9f5126b to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #138 +/- ## ======================================= Coverage 77.63% 77.63% ======================================= Files 13 13 Lines 322 322 ======================================= Hits 250 250 Misses 72 72 ```

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[tmigot]

@abelsiqueira Do you have any idea about how to fix the doc build here?