Fix assumption in ScriptItemProcessorTests.testItemBinding

This test fails on Java 15 because the Javascript engine
has been removed in Java 15 (JEP 372).

This commit updates the test to assume that the JavaScript
engine is provided to the JVM through a factory (similar
to other tests).

spring-batch-infrastructure/src/test/java/org/springframework/batch/item/support/ScriptItemProcessorTests.java

@@ -154,6 +154,8 @@ public class ScriptItemProcessorTests {
 
 	@Test
 	public void testItemBinding() throws Exception {
+		assumeTrue(languageExists("javascript"));
+
 		ScriptItemProcessor<String, Object> scriptItemProcessor = new ScriptItemProcessor<>();
 		scriptItemProcessor.setScriptSource("foo.contains('World');", "javascript");
 		scriptItemProcessor.setItemBindingVariableName("foo");