Allow upgrade of JSON.jl compat

I'm working on a project that uses JSON.jl 1.3.0. And now I need to add packages that depend on MLFlowClient.jl, but this package [constraints](https://github.com/JuliaAI/MLFlowClient.jl/blob/main/Project.toml) JSON.jl to 0.21. Could the compatibility requirement be upgraded?