LinearAlgebra: use ≈ instead of == for tr tests in symmetric.jl

[aviatesk]

After investigating #54090, I found that the issue was not caused by the effects of checksquare, but by the use of the @simd macro within tr(::Matrix):

julia/stdlib/LinearAlgebra/src/dense.jl

Lines 373 to 380 in 0945b9d

	function tr(A::Matrix{T}) where T
	n = checksquare(A)
	t = zero(T)
	@inbounds @simd for i in 1:n
	t += A[i,i]
	end
	t
	end

While simply removing the @simd macro was considered, the strict left-to-right summation without @simd otherwise is not necessarily more accurate, so I concluded that the problem lies in the test code, which tests the (strict) equality of two different tr execution results. I have modified the test code to use ≈ instead of ==.

• fixes LinearAlgebra: unstable return value, affected by lazy string & @show in error path #54090

[dkarrasch]

Yes, testing for equality only makes sense when you implicitly assume that the exact same code path is taken (and perhaps more).