Ensure that junit-platform-launcher is on classpath

When testing with Gradle 7.6, junit-platform-launcher won't be
on the test runtime classpath unless it's declared as a dependency.
When testing with Gradle 8.x the dependency is added implicitly but
starting with Gradle 8.3 relying on this will result in a warning.

When junit-platform-launcher is absent, a failure occurs when testing
with Gradle as the class loader structure is such that JUnit tries
to load any test execution listeners, finds the listener declared in
spring-boot-actuator-autoconfigure but cannot then load the
implemented TestExecutionListener interface.

This problem is addressed by augmenting the component metadata for
spring-boot-starter-test to add a dependency on
junit-platform-launcher. This addresses the problem with
spring-boot-actuator-autoconfigure while also addressing a warning
with Gradle 8.3+.

Closes gh-43340

Author: wilkinsona

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/plugin/JavaPluginAction.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -89,6 +89,7 @@ public void execute(Project project) {
 		project.afterEvaluate(this::configureUtf8Encoding);
 		configureParametersCompilerArg(project);
 		configureAdditionalMetadataLocations(project);
+		configureSpringBootStarterTestToDependOnJUnitPlatformLauncher(project);
 	}
 
 	private void classifyJarTask(Project project) {
@@ -317,6 +318,15 @@ private void configureTestAndDevelopmentOnlyConfiguration(Project project) {
 		testImplementation.extendsFrom(testAndDevelopmentOnly);
 	}
 
+	private void configureSpringBootStarterTestToDependOnJUnitPlatformLauncher(Project project) {
+		project.getDependencies()
+			.components((components) -> components.withModule("org.springframework.boot:spring-boot-starter-test",
+					(metadata) -> metadata.withVariant("runtimeElements", (variant) -> variant.withDependencies(
+							(dependencies) -> dependencies.add("org.junit.platform:junit-platform-launcher")
+
+					))));
+	}
+
 	/**
 	 * Task {@link Action} to add additional meta-data locations. We need to use an
 	 * inner-class rather than a lambda due to