fix method ambiguity with Base.in in julia nightly Version 1.12.0-DEV…514

[OkonSamuel]

This is needed to fix some failing test in another package. See https://github.com/JuliaAI/FeatureSelection.jl/actions/runs/9059544029/job/24887362493?pr=5#step:6:523

[ablaom]

I'm happy to approve this PR after appropriate testing (see below). However, it's is essentially a patch on top of a hack, for which I am personally to blame. That said, I think there is a fair chance that the overloading of in for MLJType (which is at least 3 years old, according to the blame) was rendered redundant when I refactored the learning networks code. The only way to find out for sure, would be to remove it and locally run

• MLJBase tests
• MLJTuning tests
• MLJ#dev tests, with MLJ_TEST_INTEGRATION="true".

Is this something you would consider doing? Even if we accept the current PR, we probably want to run those tests anyway, so it's the same work really.