Fail fast with explicit error message for incompatible JDK version

If the JDK version used to compile the software is not compatible with Java 24, the build fails fast with a hint what has gone wrong.
This check happens on the 'projectsLoaded' hook.
Fix gh-46625

Signed-off-by: BenchmarkingBuffalo <[email protected]>

Author: BenchmarkingBuffalo

settings.gradle

@@ -44,6 +44,11 @@ rootProject.name="spring-boot-build"
 enableFeaturePreview("STABLE_CONFIGURATION_CACHE")
 
 settings.gradle.projectsLoaded {
+	ensureCompatibleJavaVersion -> {
+		if (!JavaVersion.current().isCompatibleWith(JavaVersion.toVersion(24))) {
+			throw new GradleException("Java 24 or newer is needed to compile. Java version used is ${JavaVersion.current().toString()}.")
+		}
+	}
 	develocity {
 		buildScan {
 			def toolchainVersion = settings.gradle.rootProject.findProperty('toolchainVersion')