`display` broken for parametric structs with `show` referencing the struct parameters

[jlbosse]

`display` broken for parametric structs with `show` referencing the struct parameters

[cjdoris]

Thanks, here's a reproducer for the underlying issue

julia> using PythonCall

julia> struct Struct3{T<:Number}
           x::T
       end

julia> function Base.show(io::IO, ::MIME"text/plain", t::Struct3{T}) where T
           print(io, t.x)
       end

julia> PythonCall.Utils.mimes_for(Struct3(5))
ERROR: TypeError: in Struct3, in T, expected T<:Number, got Type{Any}
Stacktrace:
 [1] #s2#4
   @ C:\Users\chris\.julia\dev\PythonCall\src\Utils\Utils.jl:106 [inlined]
 [2] var"#s2#4"(T::Any, ::Any, ::Any)
   @ PythonCall.Utils .\none:0
 [3] (::Core.GeneratedFunctionStub)(::UInt64, ::LineNumberNode, ::Any, ::Vararg{Any})
   @ Core .\boot.jl:602
 [4] mimes_for(x::Any)
   @ PythonCall.Utils C:\Users\chris\.julia\dev\PythonCall\src\Utils\Utils.jl:93
 [5] top-level scope
   @ REPL[3]:1