fix: merge_strategy() is an instance, not a type

[kalmarek]

This is the error I got:

ERROR: LoadError: TypeError: in <:, expected Type, got a value of type COSMO.CliqueGraphMerge
Stacktrace:
  [1] COSMO.SparsityPattern(L::SparseArrays.SparseMatrixCSC{Float64, Int64}, N::Int64, ordering::Vector{Int64}, merge_strategy::COSMO.OptionsFactory{COSMO.CliqueGraphMerge}, row_range::UnitRange{Int64}, cone_ind::Int64, nz_ind_map::SparseArrays.SparseVector{Int64, Int64})
    @ COSMO ~/.julia/packages/COSMO/74ztU/src/types.jl:200
  [2] _analyse_sparsity_pattern(ci::COSMO.ChordalInfo{Float64}, csp::Vector{Int64}, sets::Vector{COSMO.AbstractConvexSet}, C::COSMO.PsdConeTriangle{Float64}, k::Int64, psd_row_range::UnitRange{Int64}, sp_ind::Int64, merge_strategy::COSMO.OptionsFactory{COSMO.CliqueGraphMerge})
    @ COSMO ~/.julia/packages/COSMO/74ztU/src/chordal_decomposition/chordal_decomposition.jl:64
  [3] analyse_sparsity_pattern!(ci::COSMO.ChordalInfo{Float64}, csp::Vector{Int64}, sets::Vector{COSMO.AbstractConvexSet}, C::COSMO.PsdConeTriangle{Float64}, k::Int64, psd_row_range::UnitRange{Int64}, sp_ind::Int64, merge_strategy::COSMO.OptionsFactory{COSMO.CliqueGraphMerge})
    @ COSMO ~/.julia/packages/COSMO/74ztU/src/chordal_decomposition/chordal_decomposition.jl:55
  [4] find_sparsity_patterns!(ws::COSMO.Workspace{Float64})
    @ COSMO ~/.julia/packages/COSMO/74ztU/src/chordal_decomposition/chordal_decomposition.jl:47
  [5] chordal_decomposition!(ws::COSMO.Workspace{Float64})
    @ COSMO ~/.julia/packages/COSMO/74ztU/src/chordal_decomposition/chordal_decomposition.jl:18
  [6] macro expansion
    @ ./timing.jl:382 [inlined]
  [7] optimize!(ws::COSMO.Workspace{Float64})
    @ COSMO ~/.julia/packages/COSMO/74ztU/src/solver.jl:90
  [8] optimize!
    @ ~/.julia/packages/COSMO/74ztU/src/MOI_wrapper.jl:151 [inlined]
[...]

With the fix it's gone and things work as usual ;)

CC: @thinh-le