Fix error in the doc of nullspace (#42960)

Author: guberger

stdlib/LinearAlgebra/src/dense.jl

@@ -1464,7 +1464,7 @@ end
     nullspace(M, rtol::Real) = nullspace(M; rtol=rtol) # to be deprecated in Julia 2.0
 
 Computes a basis for the nullspace of `M` by including the singular
-vectors of `M` whose singular values have magnitudes greater than `max(atol, rtol*σ₁)`,
+vectors of `M` whose singular values have magnitudes smaller than `max(atol, rtol*σ₁)`,
 where `σ₁` is `M`'s largest singular value.
 
 By default, the relative tolerance `rtol` is `n*ϵ`, where `n`