fix an ambiguity

Author: mcabbott

src/rulesets/Base/broadcast.jl

@@ -241,6 +241,7 @@ rrule(::RCR, ::typeof(broadcasted), ::typeof(+), args::Number...) = rrule(+, arg
 rrule(::RCR, ::typeof(broadcasted), ::typeof(-), x::Number, y::Number) = rrule(-, x, y) |> _prepend_zero
 rrule(::RCR, ::typeof(broadcasted), ::typeof(-), x::Number) = rrule(-, x) |> _prepend_zero
 rrule(::RCR, ::typeof(broadcasted), ::typeof(*), args::Number...) = rrule(*, args...) |> _prepend_zero
+rrule(::RCR, ::typeof(broadcasted), ::typeof(*), x::Number, y::Number) = rrule(*, x, y) |> _prepend_zero  # ambiguity
 rrule(::RCR, ::typeof(broadcasted), ::typeof(Base.literal_pow), ::typeof(^), x::Number, ::Val{2}) =
     rrule(Base.literal_pow, ^, x, Val(2)) |> _prepend_zero
 rrule(::RCR, ::typeof(broadcasted), ::typeof(/), x::Number, y::Number) = rrule(/, x, y) |> _prepend_zero