SpringBoot App fails to start when it depends on thymeleaf-extras-springsecurity5 but does not have Spring Security on the classpath

Closes gh-28947

Comment From: terminux

Thanks @wilkinsona , nice suggestions. I updated the PR and it's ready for your review again.

Comment From: snicoll

@terminux thanks for making your first contribution to Spring Boot. There's no need to list all 3 classes so I've only kept what @wilkinsona suggested, see f6f5aec.