YamlPropertySourceLoader may not use the right ClassLoader to check if SnakeYAML is present

[jaminh]

Similar to issues #27071 and #27072 the YamlPropertySourceLoader does not use an alternate classloader if one is provided to the SpringApplication. The problem can be found here

spring-boot/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/env/YamlPropertySourceLoader.java

Line 46 in f06b784

if (!ClassUtils.isPresent("org.yaml.snakeyaml.Yaml", null)) {

.

[wilkinsona]

Let's roll this into #27134.

[wilkinsona]

Having gone through the possible problems listed in #27134 and some more that weren't listed, I've changed my mind about this one. I'm leaning towards just fixing this specific case and leaving the others as-is until they cause a problem for someone. IMO, the possible risk of regression outweighs the benefits at the moment.