changed the test file back to its original state

Author: mridula-s109

x-pack/plugin/rank-rrf/src/test/java/org/elasticsearch/xpack/rank/rrf/RRFRetrieverBuilderParsingTests.java

@@ -115,25 +115,16 @@ public void testRRFRetrieverParsing() throws IOException {
                   "retrievers": [
                     {
                       "test": {
-                        "value": "foobar"
+                        "value": "foo"
                       }
                     },
                     {
-                      "retriever": {
-                        "test": {
-                          "value": "foo"
-                        }
+                      "test": {
+                        "value": "bar"
                       }
-                    },
-                    {
-                      "retriever": {
-                        "test": {
-                            "value": "bar"
-                        }
-                      },
-                      "weight": 1.3
                     }
                   ],
+                  "fields": ["field1", "field2"],
                   "query": "baz",
                   "rank_window_size": 100,
                   "rank_constant": 10,