Remove boxing in pinv (#51351)

As discussed in
https://discourse.julialang.org/t/pinv-not-type-stable/103885/14, the
`tol` variable is captured which leads to it being boxed, as suggested
can be fixed by having two separate variables.

stdlib/LinearAlgebra/src/dense.jl

@@ -1483,10 +1483,10 @@ function pinv(A::AbstractMatrix{T}; atol::Real = 0.0, rtol::Real = (eps(real(flo
         return B
     end
     SVD         = svd(A)
-    tol         = max(rtol*maximum(SVD.S), atol)
+    tol2        = max(rtol*maximum(SVD.S), atol)
     Stype       = eltype(SVD.S)
     Sinv        = fill!(similar(A, Stype, length(SVD.S)), 0)
-    index       = SVD.S .> tol
+    index       = SVD.S .> tol2
     Sinv[index] .= pinv.(view(SVD.S, index))
     return SVD.Vt' * (Diagonal(Sinv) * SVD.U')
 end