Try adding JET.jl to the tests

[nathanaelbosch]

JET is now part of PkgTemplates (JuliaCI/PkgTemplates.jl#432), so maybe their default JET test should be in our test suite too:

JET.test_package(ProbNumDiffEq; target_defined_modules = true)

[nathanaelbosch]

Just tried this. Unfortunately I get one error that I don't know how to fix:

julia> JET.test_package(ProbNumDiffEq; target_defined_modules=true)
JET-test failed at /home/nbosch/.julia/packages/JET/V1CGm/src/JET.jl:1185
  Expression: (JET.report_package)(ProbNumDiffEq; toplevel_logger = nothing, target_defined_modules = true)
  ═════ 1 possible error found ═════
  ┌ apply_recipe(plotattributes::AbstractDict{Symbol, Any}, sol::ProbNumDiffEq.AbstractProbODESolution) @ ProbNumDiffEq /home/nbosch/.julia/packages/RecipesBase/BRe07/src/RecipesBase.jl:298
  │ no matching method found `is_key_supported(::Symbol)`: (RecipesBase).is_key_supported::typeof(RecipesBase.is_key_supported)(:idxs)
  └────────────────────

ERROR: There was an error during testing