Use a relative tolerance in the basis-function frequency-response test

For the Kautz basis with poles up to 1e3 rad/s, the absolute difference between the two frequency-response computations exceeded 1e-10 for about 70% of the random coefficient vectors with ControlSystemsBase 1.22, while the relative difference was at most 2e-13.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: baggepinnen

test/test_basis_functions.jl

@@ -9,7 +9,7 @@ for basis in [kautz(av), laguerre(1,n), laguerre_oo(1,n), adhocbasis(av)]
     F = sum_basis(basis, p)
     fr1 = freqresp(F, w) |> vec
     fr2 = freqresp(tf(1), basis, w, p) |> vec
-    @test norm(fr1-fr2) < 1e-10
+    @test norm(fr1-fr2) < 1e-10*norm(fr1)
     @test basislength(basis) == n
 end
 basis = laguerre_oo(1,n)