Register Logback StatusListener when using custom Logback file

Update `LogbackLoggingSystem` so that the `OnErrorConsoleStatusListener`
is also registered when loading a custom Logback configuration file.

See gh-43931

Signed-off-by: Dmytro Nosan <dimanosan@gmail.com>

spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-structured-logging/src/main/resources/application.properties

@@ -10,3 +10,7 @@ logging.structured.format.console=smoketest.structuredlogging.CustomStructuredLo
 #---
 spring.config.activate.on-profile=on-error
 logging.structured.json.customizer=smoketest.structuredlogging.DuplicateJsonMembersCustomizer
+#---
+logging.config=classpath:custom-logback.xml
+spring.config.activate.on-profile=on-error-custom-logback-file
+logging.structured.json.customizer=smoketest.structuredlogging.DuplicateJsonMembersCustomizer

spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-structured-logging/src/main/resources/custom-logback.xml

@@ -0,0 +1,11 @@
+<configuration>
+	<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+		<encoder class="org.springframework.boot.logging.logback.StructuredLogEncoder">
+			<format>ecs</format>
+			<charset>UTF-8</charset>
+		</encoder>
+	</appender>
+	<root level="INFO">
+		<appender-ref ref="STDOUT"/>
+	</root>
+</configuration>

spring-boot-tests/spring-boot-smoke-tests/spring-boot-smoke-test-structured-logging/src/test/java/smoketest/structuredlogging/SampleStructuredLoggingApplicationTests.java

@@ -71,4 +71,11 @@ class SampleStructuredLoggingApplicationTests {
 		assertThat(output).contains("The name 'test' has already been written");
 	}
 
+	@Test
+	void shouldCaptureCustomizerErrorWhenUsingCustomLogbackFile(CapturedOutput output) {
+		SampleStructuredLoggingApplication
+			.main(new String[] { "--spring.profiles.active=on-error-custom-logback-file" });
+		assertThat(output).contains("The name 'test' has already been written");
+	}
+
 }