tests for rrule(prod, ::Symmetric) are disabled because they fail

[oxinabox]

This was introduced with @test_skip in https://github.com/JuliaDiff/ChainRules.jl/pull/335 I think maybe we just forgot to debug and fix it. Not sure why it fails, could be a problem with ChainRulesTestUtils/FiniteDifferences.jl (I suspect in particular it maybe be that FiniteDifferences is bad at structured matrixes)

But so we don't complete lose track, i have openned this issue

https://github.com/JuliaDiff/ChainRules.jl/blob/4ad975826ea0639ad709aeb36cc5051b6bf82eaa/test/rulesets/Base/mapreduce.jl#L103-L104