LinearAlgebra: use ≈ instead of == for tr tests in symmetric.jl (#55143)

After investigating JuliaLang/julia#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)`:

https://github.com/JuliaLang/julia/blob/0945b9d7740855c82a09fed42fbf6bc561e02c77/stdlib/LinearAlgebra/src/dense.jl#L373-L380

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 #54090

Author: aviatesk

stdlib/LinearAlgebra/test/symmetric.jl

@@ -223,8 +223,8 @@ end
 
         @testset "linalg unary ops" begin
             @testset "tr" begin
-                @test tr(asym) == tr(Symmetric(asym))
-                @test tr(aherm) == tr(Hermitian(aherm))
+                @test tr(asym) ≈ tr(Symmetric(asym))
+                @test tr(aherm) ≈ tr(Hermitian(aherm))
             end
 
             @testset "isposdef[!]" begin