Polish "Use diamond operator where feasible"

See gh-31916

spring-context/src/test/java/org/springframework/scheduling/annotation/AsyncResultTests.java

@@ -42,7 +42,6 @@ public class AsyncResultTests {
 			public void onSuccess(String result) {
 				values.add(result);
 			}
-
 			@Override
 			public void onFailure(Throwable ex) {
 				throw new AssertionError("Failure callback not expected: " + ex, ex);
@@ -65,7 +64,6 @@ public class AsyncResultTests {
 			public void onSuccess(String result) {
 				throw new AssertionError("Success callback not expected: " + result);
 			}
-
 			@Override
 			public void onFailure(Throwable ex) {
 				values.add(ex);