Restrict "validateMultiReleaseJar" task to Java 25+

This commit configures the "validateMultiReleaseJar" Gradle task only if
the current Java runtime for Gradle is 25+.

Closes gh-35850

buildSrc/src/main/java/org/springframework/build/multirelease/MultiReleaseJarPlugin.java

@@ -18,6 +18,7 @@ package org.springframework.build.multirelease;
 
 import javax.inject.Inject;
 
+import org.gradle.api.JavaVersion;
 import org.gradle.api.Plugin;
 import org.gradle.api.Project;
 import org.gradle.api.artifacts.ConfigurationContainer;
@@ -64,10 +65,12 @@ public class MultiReleaseJarPlugin implements Plugin<Project> {
 				dependencies,
 				objects);
 
-		TaskProvider<MultiReleaseJarValidateTask> validateJarTask = tasks.register(VALIDATE_JAR_TASK_NAME, MultiReleaseJarValidateTask.class, (task) -> {
-			task.getJar().set(tasks.named("jar", Jar.class).flatMap(AbstractArchiveTask::getArchiveFile));
-			task.getJavaLauncher().set(task.getJavaToolchainService().launcherFor(spec -> spec.getLanguageVersion().set(JavaLanguageVersion.of(25))));
-		});
-		tasks.named("check", task -> task.dependsOn(validateJarTask));
+		if (JavaVersion.current().isCompatibleWith(JavaVersion.VERSION_25)) {
+			TaskProvider<MultiReleaseJarValidateTask> validateJarTask = tasks.register(VALIDATE_JAR_TASK_NAME, MultiReleaseJarValidateTask.class, (task) -> {
+				task.getJar().set(tasks.named("jar", Jar.class).flatMap(AbstractArchiveTask::getArchiveFile));
+				task.getJavaLauncher().set(task.getJavaToolchainService().launcherFor(spec -> spec.getLanguageVersion().set(JavaLanguageVersion.of(25))));
+			});
+			tasks.named("check", task -> task.dependsOn(validateJarTask));
+		}
 	}
 }

buildSrc/src/test/java/org/springframework/build/multirelease/MultiReleaseJarPluginTests.java

@@ -29,6 +29,8 @@ import org.gradle.testkit.runner.GradleRunner;
 import org.gradle.testkit.runner.UnexpectedBuildFailure;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.DisabledForJreRange;
+import org.junit.jupiter.api.condition.JRE;
 import org.junit.jupiter.api.io.TempDir;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -122,6 +124,7 @@ public class MultiReleaseJarPluginTests {
 	}
 
 	@Test
+	@DisabledForJreRange(max = JRE.JAVA_24, disabledReason = "'jar --validate' is available as of Java 25")
 	void validateJar() throws IOException {
 		writeBuildFile("""
 				plugins {