Reduce eager task creation in the build

[larsgrefer]

Like #29762, but for the spring-boot build itself.

Before: https://scans.gradle.com/s/a74gck4jmky7w/performance/configuration#summary-tasks-not-created
After: https://scans.gradle.com/s/47hdj3xzmn3bw/performance/configuration#summary-tasks-not-created

[wilkinsona]

Thanks, Lars. Unfortunately, these changes seem to expose a bug (or some misconfiguration in our build) where a ConcurrentModificationException is thrown. Some experimentation suggests that the problem's been fixed in Gradle 7.x but I am not 100% sure as I don't fully understand the failure.

We haven't really had any significant problems with the time taken to configure tasks so I don't think we can really justify potentially destabilising the build at this time. Thanks anyway.

If it's any consolation, looking at this did make me realise that spring-io/spring-javaformat#319 would be a good thing to do. In Spring Boot's build, the Java Format Plugin's eagerly creating over 1000 tasks so we should see a significant reduction once 0.0.32 is released and Boot's build has been upgraded.