fix deprecation warning

[ArnoStrouwen]

@nograd is being deprecated. However, seems strange, this needs to be non-differentiable in any case?

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (b66096e) 78.00% compared to head (d1c7321) 78.12%. Report is 4 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #462 +/- ## ========================================== + Coverage 78.00% 78.12% +0.12% ========================================== Files 23 23 Lines 3155 3155 ========================================== + Hits 2461 2465 +4 + Misses 694 690 -4 ```

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[ArnoStrouwen]

@oxinabox do you know if these method ambiguities are something to worry about? And how to best fix them? https://github.com/SciML/Surrogates.jl/actions/runs/7435983790/job/20231942821?pr=462#step:6:833

[oxinabox]

Looks like a bug in ChainRulesCore. I don't understand why they are only showing up recently. There is nothing for you to do about them here. I will open a PR presently to fix them in ChainRulesCore

[ArnoStrouwen]

@sathvikbhagavan I don't see this error locally. Is this another stochastic result? https://github.com/SciML/Surrogates.jl/actions/runs/7498946122/job/20414889506?pr=462#step:6:1897

[sathvikbhagavan]

@sathvikbhagavan I don't see this error locally. Is this another stochastic result? SciML/Surrogates.jl/actions/runs/7498946122/job/20414889506?pr=462#step:6:1897

Yes, it is indeed stochastic. It happens because one of the test cluster which is sampled contains no points.

[sathvikbhagavan]

I was thinking of fixing it such that if any test cluster is empty, it uses training points for obtaining the best model for that cluster. I will make a PR for it shortly.

[ArnoStrouwen]

@ChrisRackauckas, I think this is ready. The remaining stochastic error should be looked into separately.