Fix NPE for RabbitAccessor.observationRegistry

When observation is enabled on component, but no `ObservationRegistry` bean in the application context,
we must fall back to the default one `ObservationRegistry.NOOP`

(cherry picked from commit 95d292a297)

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/connection/RabbitAccessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -33,6 +33,7 @@ import io.micrometer.observation.ObservationRegistry;
  * @author Mark Fisher
  * @author Dave Syer
  * @author Gary Russell
+ * @author Artem Bilan
  */
 public abstract class RabbitAccessor implements InitializingBean {
 
@@ -122,7 +123,7 @@ public abstract class RabbitAccessor implements InitializingBean {
 		if (appContext != null) {
 			ObjectProvider<ObservationRegistry> registry =
 					appContext.getBeanProvider(ObservationRegistry.class);
-			this.observationRegistry = registry.getIfUnique();
+			this.observationRegistry = registry.getIfUnique(() -> this.observationRegistry);
 		}
 	}