Incorrect capture of anonymous function with typed arguments

[MilesCranmer]

This is Julia 1.11:

julia> using MacroTools: splitdef

julia> splitdef(:((a::Int; b=2) -> a + b))
ERROR: AssertionError: Not a function definition: begin
        a::Int
        #= REPL[3]:1 =#
        b = 2
    end->begin
        #= REPL[3]:1 =#
        a + b
    end
Stacktrace:
 [1] splitdef(fdef::Expr)
   @ MacroTools ~/.julia/packages/MacroTools/CJmbb/src/utils.jl:317
 [2] top-level scope
   @ REPL[3]:1

[MilesCranmer]

I've got a fix! @cstjean. Want me to make a PR?

[MilesCranmer]

@cstjean added in #210