[BUG] demo not working in julia 1.6

[xgdgsc]

Describe the bug
demo at https://comonicon.org/stable/project/

module Demo

using Comonicon

@cast mycmd1(arg; option="Sam") = println("cmd1: arg=", arg, "option=", option)
@cast mycmd2(arg; option="Sam") = println("cmd2: arg=", arg, "option=", option)

"""
a module
"""
module Cmd3

using Comonicon

@cast mycmd4(arg) = println("cmd4: arg=", arg)

end # module

@cast Cmd3

"""
my demo Comonicon CLI project.
"""
@main

end # module

only works in julia 1.7

Version of the package:
julia> Pkg.status()
Status ~/Documents/tmp/Project.toml
[863f3e99] Comonicon v0.12.8

To Reproduce
Steps to reproduce the behavior:

1. Go to julia REPL
2. paste Demo code

Expected behavior
work

gives errors:

ERROR: MethodError: no method matching IOContext(::IOBuffer, ::Tuple{Pair{Symbol, Bool}, Pair{Symbol, Tuple{Int64, Int64}}})
Closest candidates are:
  IOContext(::IO) at show.jl:245
  IOContext(::IO, ::Base.ImmutableDict) at show.jl:238
  IOContext(::IO, ::Pair) at show.jl:247
  ...
Stacktrace:
 [1] sprint(f::Function, args::Markdown.MD; context::Tuple{Pair{Symbol, Bool}, Pair{Symbol, Tuple{Int64, Int64}}}, sizehint::Int64)
   @ Base ./strings/io.jl:103
 [2] md_to_string(md::Markdown.MD)
   @ Comonicon ~/.julia/packages/Comonicon/kRHtu/src/frontend/markdown.jl:176
 [3] read_description(md::Markdown.MD)
   @ Comonicon ~/.julia/packages/Comonicon/kRHtu/src/frontend/markdown.jl:105
 [4] split_docstring(m::Module)
   @ Comonicon ~/.julia/packages/Comonicon/kRHtu/src/frontend/markdown.jl:18
 [5] cast(m::Module, name::String, line::LineNumberNode)
   @ Comonicon ~/.julia/packages/Comonicon/kRHtu/src/frontend/cast.jl:490
 [6] top-level scope
   @ ~/.julia/packages/Comonicon/kRHtu/src/frontend/cast.jl:364

in 1.6. In 1.7 it works.