Fix FileSettingsRoleMappingUpgradeIT assertions (#115422)

Fixes some faulty assertions in an upgrade test. Test failures only
manifest on the 8.16 branch since 9.x does not qualify for these upgrade
tests, and the change is not backported to 8.17 yet (unrelated CI
failures).

I validated this works by running it locally from the 8.16 branch.

Resolves: #115410
Resolves: #115411

qa/rolling-upgrade/src/javaRestTest/java/org/elasticsearch/upgrades/FileSettingsRoleMappingUpgradeIT.java

@@ -25,12 +25,10 @@
 
 import java.io.IOException;
 import java.util.List;
-import java.util.Map;
 import java.util.function.Supplier;
 
-import static org.hamcrest.Matchers.contains;
 import static org.hamcrest.Matchers.equalTo;
-import static org.hamcrest.Matchers.instanceOf;
+import static org.hamcrest.Matchers.hasItem;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.not;
 import static org.hamcrest.Matchers.nullValue;
@@ -104,15 +102,17 @@ public void testRoleMappingsAppliedOnUpgrade() throws IOException {
             // the nodes have all been upgraded. Check they re-processed the role mappings in the settings file on
             // upgrade
             Request clusterStateRequest = new Request("GET", "/_cluster/state/metadata");
-            List<Object> roleMappings = new XContentTestUtils.JsonMapView(entityAsMap(client().performRequest(clusterStateRequest))).get(
-                "metadata.role_mappings.role_mappings"
+            List<Object> clusterStateRoleMappings = new XContentTestUtils.JsonMapView(
+                entityAsMap(client().performRequest(clusterStateRequest))
+            ).get("metadata.role_mappings.role_mappings");
+            assertThat(clusterStateRoleMappings, is(not(nullValue())));
+            assertThat(clusterStateRoleMappings.size(), equalTo(1));
+
+            assertThat(
+                entityAsMap(client().performRequest(new Request("GET", "/_security/role_mapping"))).keySet(),
+                // TODO change this to `contains` once the clean-up migration work is merged
+                hasItem("everyone_kibana-read-only-operator-mapping")
             );
-            assertThat(roleMappings, is(not(nullValue())));
-            assertThat(roleMappings.size(), equalTo(1));
-            assertThat(roleMappings, is(instanceOf(Map.class)));
-            @SuppressWarnings("unchecked")
-            Map<String, Object> roleMapping = (Map<String, Object>) roleMappings;
-            assertThat(roleMapping.keySet(), contains("everyone_kibana-read-only-operator-mapping"));
         }
     }
 }