Ensure sap_mnt is not mounted on observer

Author: Marges, RSY (Rick)

deploy/ansible/roles-sap-os/2.6-sap-mounts/tasks/2.6.0-afs-mounts.yaml

@@ -351,7 +351,7 @@
 
   when:
     - scs_high_availability
-    - node_tier != 'hana'
+    - node_tier not in ['hana' , 'observer']
     - sap_mnt is defined
 
 - name:                                "AFS Mount: usr/sap/{{ sap_sid | upper }}/SYS"