Fail on nightly (Julia 1.6)

[akabla]

RHEOS is currently failing on nightly.

This does not seem to be RHEOS related.
The error is linked to the file dispatch.jl in MutableArithmetics, and to the function _iszero called there.

The file dispatch.jl currently states next to the _iszero call:

# This was fixed in https://github.com/JuliaLang/julia/pull/36194 but then reverted.
# Fixed again in https://github.com/JuliaLang/julia/pull/38789/ but not merged yet.
# To determine whether the funtion is zero preserving, `LinearAlgebra` calls
# `zero` on the `eltype` of the broadcasted object and then check `_iszero`.
# `_iszero(x)` redirects to `iszero(x)` for numbers and to `x == 0` otherwise.
# `x == 0` returns false for types that implement `iszero` but not `==` such as
# `DummyBigInt` and MOI functions.
LinearAlgebra._iszero(x::AbstractMutable) = iszero(x)

We may want to check this out.
JuliaLang/julia#38789

Hopefully fixes will make their way to us.