Array `getindex` rule unable to handle Zero types and `NotImplemented`

I've been revisiting https://github.com/FluxML/Zygote.jl/pull/1328 as part of a larger PR, and discovered this behaviour while running https://github.com/FluxML/Zygote.jl/blob/108e5a19d8fa7187f6eaece7a142c48d71dfd0d2/test/chainrules.jl#L275.

MWE:

julia> _, back = rrule(getindex, [1], 1)
(1, ChainRules.var"#getindex_pullback#1601"{Vector{Int64}, Tuple{Int64}, Tuple{NoTangent}}([1], (1,), (NoTangent(),)))

julia> gs = back(@not_implemented("test"))
(NoTangent(), InplaceableThunk(ChainRules.var"#..., Thunk(ChainRules.var"#...)), NoTangent())

julia> unthunk(gs[2])
ERROR: MethodError: Cannot `convert` an object of type Bool to an object of type ChainRulesCore.NotImplemented
Closest candidates are:
  convert(::Type{T}, ::T) where T at Base.jl:61
  ChainRulesCore.NotImplemented(::Any, ::Any, ::Any) at ~/.julia/packages/ChainRulesCore/a4mIA/src/tangent_types/notimplemented.jl:30
Stacktrace:
 [1] fill!(dest::Vector{ChainRulesCore.NotImplemented}, x::Bool)
   @ Base ./array.jl:351
 [2] _setindex_zero(x::Vector{Int64}, dy::ChainRulesCore.NotImplemented, inds::Int64)
   @ ChainRules ~/.julia/packages/ChainRules/bEtjZ/src/rulesets/Base/indexing.jl:104
 [3] ∇getindex(x::Vector{Int64}, dy::ChainRulesCore.NotImplemented, inds::Int64)
   @ ChainRules ~/.julia/packages/ChainRules/bEtjZ/src/rulesets/Base/indexing.jl:88
 [4] (::ChainRules.var"#1603#1605"{Vector{Int64}, ChainRulesCore.NotImplemented, Tuple{Int64}})()
   @ ChainRules ~/.julia/packages/ChainRules/bEtjZ/src/rulesets/Base/indexing.jl:73
 [5] unthunk
   @ ~/.julia/packages/ChainRulesCore/a4mIA/src/tangent_types/thunks.jl:204 [inlined]
 [6] unthunk(x::InplaceableThunk{Thunk{ChainRules.var"#1603#1605"{Vector{Int64}, ChainRulesCore.NotImplemented, Tuple{Int64}}}, ChainRules.var"#1602#1604"{Vector{Int64}, ChainRulesCore.NotImplemented, Tuple{Int64}}})
   @ ChainRulesCore ~/.julia/packages/ChainRulesCore/a4mIA/src/tangent_types/thunks.jl:237
 [7] top-level scope
   @ REPL[11]:1

julia> _, back = rrule(getindex, [1], [1])
([1], ChainRules.var"#getindex_pullback#1601"{Vector{Int64}, Tuple{Vector{Int64}}, Tuple{NoTangent}}([1], ([1],), (NoTangent(),)))

julia> gs = back([NoTangent()])
(NoTangent(), InplaceableThunk(ChainRules.var"#..., Thunk(ChainRules.var"#...)), NoTangent())

julia> unthunk(gs[2])
ERROR: MethodError: Cannot `convert` an object of type Bool to an object of type NoTangent
Closest candidates are:
  convert(::Type{T}, ::T) where T at Base.jl:61
Stacktrace:
 [1] fill!(dest::Vector{NoTangent}, x::Bool)
   @ Base ./array.jl:351
 [2] _setindex_zero(x::Vector{Int64}, dy::Vector{NoTangent}, inds::Vector{Int64})
   @ ChainRules ~/.julia/packages/ChainRules/bEtjZ/src/rulesets/Base/indexing.jl:105
 [3] ∇getindex(x::Vector{Int64}, dy::Vector{NoTangent}, inds::Vector{Int64})
   @ ChainRules ~/.julia/packages/ChainRules/bEtjZ/src/rulesets/Base/indexing.jl:88
 [4] (::ChainRules.var"#1603#1605"{Vector{Int64}, Vector{NoTangent}, Tuple{Vector{Int64}}})()
   @ ChainRules ~/.julia/packages/ChainRules/bEtjZ/src/rulesets/Base/indexing.jl:73
 [5] unthunk
   @ ~/.julia/packages/ChainRulesCore/a4mIA/src/tangent_types/thunks.jl:204 [inlined]
 [6] unthunk(x::InplaceableThunk{Thunk{ChainRules.var"#1603#1605"{Vector{Int64}, Vector{NoTangent}, Tuple{Vector{Int64}}}}, ChainRules.var"#1602#1604"{Vector{Int64}, Vector{NoTangent}, Tuple{Vector{Int64}}}})
   @ ChainRulesCore ~/.julia/packages/ChainRulesCore/a4mIA/src/tangent_types/thunks.jl:237
 [7] top-level scope
   @ REPL[14]:1

The lines at fault are https://github.com/JuliaDiff/ChainRules.jl/blob/4ee4ef5ffa86809885a944d8167503b7e2e550fa/src/rulesets/Base/indexing.jl#L104-L105. I would imagine considering x's eltype in the final array would be beneficial, but I'm not familiar enough with all the edge cases to be sure. Maybe the correct solution is to catch this at a higher level.

Start with test/chainrules.jl around the referenced line and reproduce both MWE cases. Then inspect src/rulesets/Base/indexing.jl at lines 88 and 104-105, focusing on how _setindex_zero handles NotImplemented and NoTangent; done means the pullback can be unthunked for both scalar and array indices without conversion errors.