Work around Spring Framework cache pollution bug

Update `SpringApplication` to work around `SpringFactoriesLoader`
cache pollution by loading factories using a `null` class loader.

See https://github.com/spring-projects/spring-framework/pull/34732
for details.

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/SpringApplication.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.
@@ -480,7 +480,7 @@ public class SpringApplication {
 	}
 
 	private <T> List<T> getSpringFactoriesInstances(Class<T> type, ArgumentResolver argumentResolver) {
-		return SpringFactoriesLoader.forDefaultResourceLocation(getClassLoader()).load(type, argumentResolver);
+		return SpringFactoriesLoader.forDefaultResourceLocation(getClassLoader(null)).load(type, argumentResolver);
 	}
 
 	private ConfigurableEnvironment getOrCreateEnvironment() {
@@ -715,10 +715,11 @@ public class SpringApplication {
 	 * @return a ClassLoader (never null)
 	 */
 	public ClassLoader getClassLoader() {
-		if (this.resourceLoader != null) {
-			return this.resourceLoader.getClassLoader();
-		}
-		return ClassUtils.getDefaultClassLoader();
+		return getClassLoader(ClassUtils.getDefaultClassLoader());
+	}
+
+	private ClassLoader getClassLoader(ClassLoader fallback) {
+		return (this.resourceLoader != null) ? this.resourceLoader.getClassLoader() : fallback;
 	}
 
 	/**