Change test manage share server with invalid id

Changes Tempest test according to Manila manager change 857960 to
prevent a share server to be managed only if its identifier is a
suffix of any existing identifier.

Closes-bug: #1982429
Change-Id: I14df0c9c7326ac49274699dc0ef1adb99570784b
diff --git a/manila_tempest_tests/tests/api/admin/test_share_servers_manage_negative.py b/manila_tempest_tests/tests/api/admin/test_share_servers_manage_negative.py
index 1e9073d..09a40d9 100644
--- a/manila_tempest_tests/tests/api/admin/test_share_servers_manage_negative.py
+++ b/manila_tempest_tests/tests/api/admin/test_share_servers_manage_negative.py
@@ -333,7 +333,8 @@
             invalid_params)
 
         # try with part of the identifier
-        invalid_params['identifier'] = share_server['identifier'].split("-")[2]
+        invalid_params['identifier'] = (
+            share_server['identifier'].split("-")[-1])
 
         self.assertRaises(
             lib_exc.BadRequest,