`Assertion cycle == depth' failed` when testing AxisKeys

[KristofferC]

When testing AxisKeys it asserts with Assertion cycle == depth' failed:

Test Summary:            | Pass  Total   Time
fast findfirst & findall |  448    448  11.4s
julia: /source/src/gf.c:3429: sort_mlmatches: Assertion `cycle == depth' failed.

[30] signal (6.-6): Aborted
in expression starting at /home/pkgeval/.julia/packages/AxisKeys/QsNqy/test/runtests.jl:31

[maleadt]

This one is tough to reduce; removing code makes the bug not occur always anymore. The following MWE crashes every so often, and it seems more likely when running with --compiled-modules=false:

module AxisKeys
using Base: @propagate_inbounds, OneTo, RefValue
struct KeyedArray{T,N,AT,KT} <: AbstractArray{T,N} end
const KeyedVector = KeyedArray
const KeyedMatrix = KeyedArray
const KeyedVecOrMat = Union{KeyedVector, KeyedMatrix}
using NamedDims
Base.vcat(A::AbstractVecOrMat, B::KeyedVecOrMat, Cs::AbstractVecOrMat...) = nothing
end

using Test
detect_ambiguities(AxisKeys, Base)

[maleadt]

Bisected to ac1cb1c, so #49664 (cc @vtjnash).

The method lookup that fails:

type = Tuple{typeof(Base.vcat), AbstractArray{T, 1} where T, AxisKeys.KeyedArray{T, 1, AT, KT} where KT where AT where T, Vararg{AbstractArray{T, 1} where T}}
Base._methods_by_ftype(type, -1, Base.get_world_counter())

... so this can be used instead of detect_ambiguities (although the import of Test still seems required).