(fix): enable build index image

Author: AjayJagan

.tekton/ray-cuda-push.yaml

@@ -115,7 +115,7 @@ spec:
       description: Build a source image.
       name: build-source-image
       type: string
-    - default: "false"
+    - default: "true"
       description: Add built image into an OCI image index
       name: build-image-index
       type: string