Re-bump tolerance in test_mass_mat_trig (old sym)

As requested by @matthiasdiener in
https://github.com/inducer/grudge/pull/249#pullrequestreview-933685048

test/test_grudge_sym_old.py

@@ -144,7 +144,7 @@ def test_mass_mat_trig(actx_factory, ambient_dim, discr_tag):
 
     num_integral_1 = np.dot(ones_volm, actx.to_numpy(flatten(mass_op(f=f_quad))))
     err_1 = abs(num_integral_1 - true_integral)
-    assert err_1 < 6e-9, err_1
+    assert err_1 < 9e-9, err_1
 
     num_integral_2 = np.dot(f_volm, actx.to_numpy(flatten(mass_op(f=ones_quad))))
     err_2 = abs(num_integral_2 - true_integral)