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

[oxinabox]

This was introduced with @test_skip in #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

ChainRules.jl/test/rulesets/Base/mapreduce.jl

Lines 103 to 104 in 4ad9758

	@test_skip test_rrule(prod, xs ⊢ rand(T,4,4))
	@test_skip test_rrule(prod, xs ⊢ rand(T,4,4), fkwargs=(dims=2,))