Only attempt mock reset on instantiated singletons

Update ResetMocksTestExecutionListener to only attempt a mock reset when
a singleton has actually been created.

Fixes gh-5870

spring-boot-test/src/test/java/org/springframework/boot/test/mock/mockito/ResetMocksTestExecutionListenerTests.java

@@ -26,6 +26,7 @@ import org.springframework.boot.test.mock.mockito.example.ExampleService;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.Lazy;
 import org.springframework.test.context.junit4.SpringRunner;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -80,6 +81,13 @@ public class ResetMocksTestExecutionListenerTests {
 			return mock(ExampleService.class);
 		}
 
+		@Bean
+		@Lazy
+		public ExampleService fail() {
+			// gh-5870
+			throw new RuntimeException();
+		}
+
 	}
 
 }