Updates ISM to 1.2 tag in manifest (#1141)

Signed-off-by: Robert Downs <[email protected]>

manifests/1.2.0/opensearch-1.2.0.yml

@@ -40,7 +40,7 @@ components:
       - gradle:dependencies:opensearch.version
   - name: index-management
     repository: https://github.com/opensearch-project/index-management.git
-    ref: "1.2"
+    ref: tags/1.2.0.0
     checks:
       - gradle:properties:version
       - gradle:dependencies:opensearch.version