Do not name an argument _ in methods with keyword arguments

Julia 1.10 rejects such methods with "syntax: all-underscore identifier
used as rvalue", which made the package fail to load on the lowest
supported Julia version.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: baggepinnen

src/frd.jl

@@ -110,8 +110,8 @@ end
 
 ControlSystemsBase.noutputs(f::FRD) = f.r isa AbstractVector ? 1 : size(f.r, 1)
 ControlSystemsBase.ninputs(f::FRD) = f.r isa AbstractVector ? 1 : size(f.r, 2)
-ControlSystemsBase._default_freq_vector(f::Vector{<:FRD}, _; kwargs...) = f[1].w
-ControlSystemsBase._default_freq_vector(f::FRD, _; kwargs...) = f.w
+ControlSystemsBase._default_freq_vector(f::Vector{<:FRD}, ::Any; kwargs...) = f[1].w
+ControlSystemsBase._default_freq_vector(f::FRD, ::Any; kwargs...) = f.w
 function ControlSystemsBase.bode(f::FRD, w::AbstractVector = f.w; unwrap=true, kwargs...) # kwargs such as balance do not apply to frequency-response data
     w == f.w || error("Frequency vector must match the one stored in the FRD")
     angles = angle.(f.r)