ipatests: Fix for test_ipahealthcheck_ds_encryption

Nightly test failure was seen for test_ipahealthcheck_ds_encryption
The test was failing since @pytest.fixture was not specified before
the function modify_tls

Ref: https://pagure.io/freeipa/issue/8560
Reviewed-By: Mohammad Rizwan Yusuf <myusuf@redhat.com>
Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>

ipatests/test_integration/test_ipahealthcheck.py

@@ -1006,9 +1006,10 @@ class TestIpaHealthCheck(IntegrationTest):
             assert check["result"] == "CRITICAL"
             assert exception_msg in check["kw"]["exception"]
 
+    @pytest.fixture
     def modify_tls(self, restart_service):
         """
-        Modify DS tls version to TLS1.0 using dsconf tool and
+        Fixture to modify DS tls version to TLS1.0 using dsconf tool and
         revert back to the default TLS1.2
         """
         instance = realm_to_serverid(self.master.domain.realm)