change ml-commons to use 2.0 branch for 2.0 release (#1986)

Signed-off-by: Xun Zhang <[email protected]>

manifests/2.0.0/opensearch-2.0.0.yml

@@ -29,7 +29,7 @@ components:
       - gradle:dependencies:opensearch.version
   - name: ml-commons
     repository: https://github.com/opensearch-project/ml-commons.git
-    ref: main
+    ref: '2.0'
     checks:
       - gradle:properties:version
       - gradle:dependencies:opensearch.version: opensearch-ml-plugin