Fix comment

Author: mhyeon-lee

server-common/src/test/java/io/a2a/server/tasks/TaskManagerTest.java

@@ -589,7 +589,7 @@ public void testSaveTaskEventMetadataUpdateNull() throws A2AServerException {
 
     @Test
     public void testSaveTaskEventMetadataMergeExisting() throws A2AServerException {
-        // Test that metadata update overwrites existing metadata
+        // Test that metadata update merges with existing metadata
         Map<String, Object> originalMetadata = new HashMap<>();
         originalMetadata.put("original_key", "original_value");