TST: PR 18697 revisions

* add a general `xfail` to `test_maxiter_worsening()`
based on reviewer feedback--this test has just been causing
way too many problems for us

scipy/sparse/linalg/_isolve/tests/test_iterative.py

@@ -455,6 +455,7 @@ def test_zero_rhs(solver):
                 assert_allclose(x, 0, atol=1e-300)
 
 
+@pytest.mark.xfail(reason="see gh-18697")
 def test_maxiter_worsening(solver):
     if solver not in (gmres, lgmres):
         # these were skipped from the very beginning, see gh-9201; gh-14160