SOLR-14969: Prevent creating multiple cores with the same name which leads to instabilities (race condition) changed error code

solr/core/src/java/org/apache/solr/core/CoreContainer.java

@@ -1280,7 +1280,7 @@ public class CoreContainer {
         } else {
           String msg = "Already creating a core with name '" + coreName + "', call aborted '";
           log.warn(msg);
-          throw new SolrException(ErrorCode.SERVER_ERROR, msg);
+          throw new SolrException(ErrorCode.CONFLICT, msg);
         }
       }
       CoreDescriptor cd = new CoreDescriptor(coreName, instancePath, parameters, getContainerProperties(), getZkController());