Run LoaderIntegrationTests on Java 21

See gh-37359

spring-boot-tests/spring-boot-integration-tests/spring-boot-loader-tests/src/intTest/java/org/springframework/boot/loader/LoaderIntegrationTests.java

@@ -87,6 +87,7 @@ class LoaderIntegrationTests {
 		javaRuntimes.add(JavaRuntime.openJdk(JavaVersion.SEVENTEEN));
 		javaRuntimes.add(JavaRuntime.openJdk(JavaVersion.TWENTY));
 		javaRuntimes.add(JavaRuntime.oracleJdk17());
+		javaRuntimes.add(JavaRuntime.openJdkEarlyAccess(JavaVersion.TWENTY_ONE));
 		return javaRuntimes.stream().filter(JavaRuntime::isCompatible);
 	}
 
@@ -117,6 +118,13 @@ class LoaderIntegrationTests {
 			return this.name;
 		}
 
+		static JavaRuntime openJdkEarlyAccess(JavaVersion version) {
+			String imageVersion = version.toString();
+			DockerImageName image = DockerImageName.parse(String.format("openjdk:%s-ea-jdk", imageVersion));
+			return new JavaRuntime("OpenJDK Early Access " + imageVersion, version,
+					() -> new GenericContainer<>(image));
+		}
+
 		static JavaRuntime openJdk(JavaVersion version) {
 			String imageVersion = (version != JavaVersion.EIGHT) ? version.toString() : "8";
 			DockerImageName image = DockerImageName.parse("bellsoft/liberica-openjdk-debian:" + imageVersion);