MINOR: Fix flaky MetadataLoaderTest.testNoPublishEmptyImage (apache…

…#14875)

There is a race in the assertion on `capturedImages`. Since the future is signaled first, it is still possible to see an empty list. By adding to the collection first, we can ensure the assertion will succeed.

Reviewers: Reviewers: David Jacot <[email protected]>

metadata/src/test/java/org/apache/kafka/image/loader/MetadataLoaderTest.java

@@ -793,10 +793,10 @@ public String name() {
 
  @Override
  public void onMetadataUpdate(MetadataDelta delta, MetadataImage newImage, LoaderManifest manifest) {
+ capturedImages.add(newImage);
  if (!firstPublish.isDone()) {
  firstPublish.complete(null);
  }
- capturedImages.add(newImage);
  }
  };