ipatests: Look for warning into stderr instead of stdout

In https://github.com/freeipa/freeipa/pull/5855 was looking
into stdout_text for warning instead of stderr_text, hence
was failing for pki version > 10.11.0.

related: https://pagure.io/freeipa/issue/8890

Signed-off-by: Mohammad Rizwan <myusuf@redhat.com>
Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>

ipatests/test_integration/test_ipa_cert_fix.py

@@ -241,16 +241,14 @@ class TestIpaCertFix(IntegrationTest):
         # check that pki-server cert-fix command fails
         err_msg2 = ("ERROR: CalledProcessError(Command "
                     "['pki-server', 'cert-fix'")
-        warn_msg = ("WARNING: No selftests configured in "
-                    f"{paths.CA_CS_CFG_PATH} "
-                    "(selftests.container.order.startup)")
+        warn_msg = "WARNING: No selftests configured in"
 
         if (tasks.get_pki_version(self.master)
            < tasks.parse_version('10.11.0')):
             assert (err_msg1 in result.stderr_text
                     and err_msg2 in result.stderr_text)
         else:
-            assert warn_msg in result.stdout_text
+            assert warn_msg in result.stderr_text
 
     def test_expired_CA_cert(self, expire_ca_cert):
         """Test to check ipa-cert-fix when CA certificate is expired