Use beanClassLoader when checking excluded auto-configuration classes

When validating exclusions, prefer the selector's beanClassLoader for
ClassUtils.isPresent checks and fall back to the selector class loader
if the beanClassLoader is not set.

This makes presence checks consistent with the classloader context used
for loading auto-configuration candidates.

See gh-48129

Signed-off-by: linw-bai <107357009+linw-bai@users.noreply.github.com>

Author: linw-bai

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/AutoConfigurationImportSelector.java

@@ -205,8 +205,9 @@ protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, A
 
 	private void checkExcludedClasses(List<String> configurations, Set<String> exclusions) {
 		List<String> invalidExcludes = new ArrayList<>(exclusions.size());
+		ClassLoader classLoader = (this.beanClassLoader != null) ? this.beanClassLoader : getClass().getClassLoader();
 		for (String exclusion : exclusions) {
-			if (ClassUtils.isPresent(exclusion, getClass().getClassLoader()) && !configurations.contains(exclusion)) {
+			if (ClassUtils.isPresent(exclusion, classLoader) && !configurations.contains(exclusion)) {
 				invalidExcludes.add(exclusion);
 			}
 		}