Fix compatibility with OrderedSet v2

[blegat]

Fix this error:

 MethodError: no method matching getindex(::OrderedCollections.OrderedSet{Int64}, ::Int64)
    The function `getindex` exists, but no method is defined for this combination of argument types.
    Stacktrace:
      [1] psd_complete!(A::Matrix{Float64}, pattern::Clarabel.SparsityPattern)
        @ Clarabel ~/.julia/packages/Clarabel/ChSpM/src/chordal/decomposition/psd_completion.jl:75
      [2] complete!(z::SubArray{Float64, 1, Vector{Float64}, Tuple{UnitRange{Int64}}, true},
  pattern::Clarabel.SparsityPattern)
        @ Clarabel ~/.julia/packages/Clarabel/ChSpM/src/chordal/decomposition/psd_completion.jl:36
      [3] psd_completion!(chordal_info::Clarabel.ChordalInfo{Float64},
  variables::Clarabel.DefaultVariables{Float64})
        @ Clarabel ~/.julia/packages/Clarabel/ChSpM/src/chordal/decomposition/psd_completion.jl:25
      [4] decomp_reverse!(chordal_info::Clarabel.ChordalInfo{Float64}, old_vars::Clarabel.DefaultVariables{Float64},
  old_cones::Vector{Clarabel.SupportedCone}, settings::Clarabel.Settings{Float64})
        @ Clarabel ~/.julia/packages/Clarabel/ChSpM/src/chordal/decomposition/decomp.jl:54
      [5] solution_post_process!(solution::Clarabel.DefaultSolution{Float64},
  data::Clarabel.DefaultProblemData{Float64}, variables::Clarabel.DefaultVariables{Float64},
  info::Clarabel.DefaultInfo{Float64}, settings::Clarabel.Settings{Float64})
        @ Clarabel ~/.julia/packages/Clarabel/ChSpM/src/solution.jl:32

Detected in jump-dev/MathOptInterface.jl#3055

[odow]

You've already done this in #230

[blegat]

Apparently, the warning turned into an error