Align JSpecify @Nullable annotation

spring-context/src/main/java/org/springframework/context/support/DefaultLifecycleProcessor.java

@@ -248,8 +248,7 @@ public class DefaultLifecycleProcessor implements LifecycleProcessor, BeanFactor
 		return executor;
 	}
 
-	@Nullable
+	private @Nullable Long determineConcurrentStartup(int phase) {
-	private Long determineConcurrentStartup(int phase) {
 		return this.concurrentStartupForPhases.get(phase);
 	}