update test expectations

Author: lizk886

src/test/java/com/uid2/shared/attest/UidCoreClientTest.java

@@ -134,8 +134,8 @@ public void Download_Http404Error_LogsStatusCode() throws IOException, Attestati
         assertAll(
             () -> assertTrue(result.getMessage().contains("HTTP response code 404"), 
                 "Should contain HTTP status code 404"),
-            () -> assertTrue(result.getMessage().contains("Cannot download required files from UID2 core service"), 
-                "Should have customer-friendly message")
+            () -> assertTrue(result.getMessage().contains("E12: Data Download Failure"), 
+                "Should contain E12 error code")
         );
     }