Unit testing syntax `@testset let`

The new unit testing syntax on Julia 1.9 is extremely useful. For example: ```julia julia> @testset let logi = log(im) @test imag(logi) == π/2 @test !iszero(real(logi)) end Test Failed at none:3 Expression: !(iszero(real(logi))) Context: logi = 0.0 + 1.5707963267948966im ERROR: There was an error during testing ``` The downside is that it's only Julia 1.9, so I can't actually use it in my packages, as I want to maintain compatibility with Julia 1.6. So, it would be great if this syntax could be added to Compat.jl! Best, Miles