Restore 'javax.xml.bind:jaxb-api' exclusion

Restore the 'javax.xml.bind:jaxb-api' exclusion from `xmlunit-core`
which is actually required when using Maven on Java 9+.

The `CheckClasspathForUnnecessaryExclusions` cannot deal with profile
specific dependencies so an exception has been hard coded.

See gh-28332

buildSrc/src/main/java/org/springframework/boot/build/classpath/CheckClasspathForUnnecessaryExclusions.java

@@ -109,6 +109,7 @@ public class CheckClasspathForUnnecessaryExclusions extends DefaultTask {
 						.getIncoming().getArtifacts().getArtifacts().stream().map(this::getId)
 						.collect(Collectors.toList());
 				exclusions.removeAll(dependencies);
+				removeProfileExclusions(dependencyId, exclusions);
 				if (!exclusions.isEmpty()) {
 					unnecessaryExclusions.put(dependencyId, exclusions);
 				}
@@ -119,6 +120,12 @@ public class CheckClasspathForUnnecessaryExclusions extends DefaultTask {
 		}
 	}
 
+	private void removeProfileExclusions(String dependencyId, Set<String> exclusions) {
+		if ("org.xmlunit:xmlunit-core".equals(dependencyId)) {
+			exclusions.remove("javax.xml.bind:jaxb-api");
+		}
+	}
+
 	private String getExceptionMessage(Map<String, Set<String>> unnecessaryExclusions) {
 		StringBuilder message = new StringBuilder("Unnecessary exclusions detected:");
 		for (Entry<String, Set<String>> entry : unnecessaryExclusions.entrySet()) {

spring-boot-project/spring-boot-starters/spring-boot-starter-test/build.gradle

@@ -18,5 +18,7 @@ dependencies {
 	api("org.skyscreamer:jsonassert")
 	api("org.springframework:spring-core")
 	api("org.springframework:spring-test")
-	api("org.xmlunit:xmlunit-core")
+	api("org.xmlunit:xmlunit-core") {
+		exclude group: "javax.xml.bind", module: "jaxb-api"
+	}
 }