CompatHelper: bump compat for NLPModels to 0.20, (keep existing compat)

[github-actions[bot]]

This pull request changes the compat entry for the NLPModels package from 0.18, 0.19 to 0.18, 0.19, 0.20. This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry. It is your responsibility to make sure that your package tests pass before you merge this pull request.

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (5798053) 86.33% compared to head (c4040dc) 86.33%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #128 +/- ## ======================================= Coverage 86.33% 86.33% ======================================= Files 7 7 Lines 783 783 ======================================= Hits 676 676 Misses 107 107 ``` | [Impacted Files](https://app.codecov.io/gh/JuliaSmoothOptimizers/FletcherPenaltySolver.jl/pull/128?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaSmoothOptimizers) | Coverage Δ | | |---|---|---| | [src/algo.jl](https://app.codecov.io/gh/JuliaSmoothOptimizers/FletcherPenaltySolver.jl/pull/128?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaSmoothOptimizers#diff-c3JjL2FsZ28uamw=) | `77.47% <100.00%> (ø)` | |

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