reno: fix typo

follow: https://review.opendev.org/c/openstack/kolla-ansible/+/794359
trivial fix

Change-Id: I7bd24dd660939c81f15d46679454a2663137bdde

releasenotes/notes/remove-rally-deployment-6c7718e404b359a6.yaml

 ---
 upgrade:
   - |
-    The ``Rally`` project is not a serive of openstack but its client.
+    The ``Rally`` project is not a service of OpenStack but its client.
     Its images and support are removed since Xena cycle.