Depwarns on Julia 1.7 "use values(kwargs) and keys(kwargs) instead of kwargs.data and kwargs.itr"

[jaakkor2]

On Julia 1.7 JSON3 1.8.1, I see lots of warnings, and this slows down the first runs

┌ Warning: use values(kwargs) and keys(kwargs) instead of kwargs.data and kwargs.itr
│   caller = #_#67 at write.jl:118 [inlined]
└ @ Core C:\Users\jru\.julia\packages\JSON3\A0XBc\src\write.jl:118
┌ Warning: use values(kwargs) and keys(kwargs) instead of kwargs.data and kwargs.itr
│   caller = #write#68 at write.jl:131 [inlined]
└ @ Core C:\Users\jru\.julia\packages\JSON3\A0XBc\src\write.jl:131
┌ Warning: use values(kwargs) and keys(kwargs) instead of kwargs.data and kwargs.itr
│   caller = #read#30 at structs.jl:273 [inlined]
└ @ Core C:\Users\jru\.julia\packages\JSON3\A0XBc\src\structs.jl:273
┌ Warning: use values(kwargs) and keys(kwargs) instead of kwargs.data and kwargs.itr
│   caller = #_#38 at structs.jl:384 [inlined]
└ @ Core C:\Users\jru\.julia\packages\JSON3\A0XBc\src\structs.jl:384
┌ Warning: use values(kwargs) and keys(kwargs) instead of kwargs.data and kwargs.itr
│   caller = #read!#41 at structs.jl:449 [inlined]
└ @ Core C:\Users\jru\.julia\packages\JSON3\A0XBc\src\structs.jl:449
┌ Warning: use values(kwargs) and keys(kwargs) instead of kwargs.data and kwargs.itr
│   caller = #_#42 at structs.jl:493 [inlined]
└ @ Core C:\Users\jru\.julia\packages\JSON3\A0XBc\src\structs.jl:493
┌ Warning: use values(kwargs) and keys(kwargs) instead of kwargs.data and kwargs.itr
│   caller = #read#43 at structs.jl:554 [inlined]
└ @ Core C:\Users\jru\.julia\packages\JSON3\A0XBc\src\structs.jl:554

See JuliaLang/julia#39448