[BUG] `Vararg` does not work on recent Julia versions

[Jakob Nybo Nissen]

Describe the bug
A CLI function of the form:

@main foo(xs::Vararg{String}) = foreach(println, xs)

Errors with ERROR: LoadError: TypeError: in <:, expected Type, got Vararg{String}. See the full stacktrace at the bottom of this post.

Version of the package:

• Julia 1.10-beta3
• Comonicon 1.0.6

This does not happen on earlier Julia versions

To Reproduce
Execute the following script

using Comonicon
 @main foo(xs::Vararg{String}) = foreach(println, xs)

This presumably happens because Vararg{String} isa Type returns false on Julia 1.7 and later.

Full stack trace:

ERROR: LoadError: TypeError: in <:, expected Type, got Vararg{String}
Stacktrace:
  [1] ignore_type(type::Core.TypeofVararg)
    @ Comonicon.AST ~/.julia/packages/Comonicon/AXDxW/src/ast/printing.jl:2
  [2] print_cmd(io::IOBuffer, arg::Comonicon.AST.Argument, t::Comonicon.AST.Terminal)
    @ Comonicon.AST ~/.julia/packages/Comonicon/AXDxW/src/ast/printing.jl:95
  [3] print_signature
    @ Comonicon.AST ~/.julia/packages/Comonicon/AXDxW/src/ast/printing.jl:179 [inlined]
  [4] print_with_brief(f::typeof(Comonicon.AST.print_signature), io::IOContext{IOBuffer}, cmd::Comonicon.AST.Argument, t::Comonicon.AST.Terminal)
    @ Comonicon.AST ~/.julia/packages/Comonicon/AXDxW/src/ast/printing.jl:268
  [5] print_sig_brief
    @ Comonicon.AST ~/.julia/packages/Comonicon/AXDxW/src/ast/printing.jl:259 [inlined]
  [6] print_body(io::IOContext{IOBuffer}, cmd::Comonicon.AST.LeafCommand, t::Comonicon.AST.Terminal)
    @ Comonicon.AST ~/.julia/packages/Comonicon/AXDxW/src/ast/printing.jl:225
  [7] print_cmd(io::IOContext{IOBuffer}, cmd::Comonicon.AST.LeafCommand, t::Comonicon.AST.Terminal)
    @ Comonicon.AST ~/.julia/packages/Comonicon/AXDxW/src/ast/printing.jl:152
  [8] print_cmd(io::IOContext{IOBuffer}, cmd::Comonicon.AST.LeafCommand)
    @ Comonicon.AST ~/.julia/packages/Comonicon/AXDxW/src/ast/printing.jl:86
  [9] _sprint(f::Function, args::Comonicon.AST.LeafCommand; color::Bool, displaysize::Tuple{Int64, Int64})
    @ Comonicon ~/.julia/packages/Comonicon/AXDxW/src/compat.jl:10
 [10] _sprint
    @ Comonicon ~/.julia/packages/Comonicon/AXDxW/src/compat.jl:7 [inlined]
 [11] #help_str#1
    @ Comonicon.JuliaExpr ~/.julia/packages/Comonicon/AXDxW/src/codegen/julia.jl:10 [inlined]
 [12] help_str
    @ Comonicon.JuliaExpr ~/.julia/packages/Comonicon/AXDxW/src/codegen/julia.jl:9 [inlined]
 [13] print_help_str(x::Comonicon.AST.LeafCommand, ctx::Comonicon.JuliaExpr.EmitContext)
    @ Comonicon.JuliaExpr ~/.julia/packages/Comonicon/AXDxW/src/codegen/julia.jl:33
 [14] emit_help(x::Comonicon.AST.LeafCommand, ctx::Comonicon.JuliaExpr.EmitContext, ptr::Int64; color::Bool)
    @ Comonicon.JuliaExpr ~/.julia/packages/Comonicon/AXDxW/src/codegen/julia.jl:40
 [15] emit_help
    @ Comonicon.JuliaExpr ~/.julia/packages/Comonicon/AXDxW/src/codegen/julia.jl:40 [inlined]
 [16] emit_body(cmd::Comonicon.AST.LeafCommand, ctx::Comonicon.JuliaExpr.EmitContext, ptr::Int64)
    @ Comonicon.JuliaExpr ~/.julia/packages/Comonicon/AXDxW/src/codegen/julia.jl:150
 [17] emit_body(cmd::Comonicon.AST.NodeCommand, ctx::Comonicon.JuliaExpr.EmitContext, ptr::Int64)
    @ Comonicon.JuliaExpr ~/.julia/packages/Comonicon/AXDxW/src/codegen/julia.jl:133
 [18] emit(cmd::Comonicon.AST.Entry, configs::Comonicon.JuliaExpr.Configs, ptr::Int64)
    @ Comonicon.JuliaExpr ~/.julia/packages/Comonicon/AXDxW/src/codegen/julia.jl:86
 [19] top-level scope
    @ ~/.julia/packages/Comonicon/AXDxW/src/frontend/cast.jl:449
 [20] include
    @ Base ./Base.jl:489 [inlined]
 [21] include_package_for_output(pkg::Base.PkgId, input::String, depot_path::Vector{String}, dl_load_path::Vector{String}, load_path::Vector{String}, concrete_deps::Vector{Pair{Base.PkgId, UInt128}}, source::String)
    @ Base ./loading.jl:2216
 [22] top-level scope
    @ stdin:3