Fix code sample that uses deprecated StepBuilderFactory

Backported from b020da4

Issue #4582

spring-batch-docs/src/main/asciidoc/scalability.adoc

@@ -338,8 +338,8 @@ configuration:
 [source, java, role="javaContent"]
 ----
 @Bean
-public Step step1Manager() {
-    return stepBuilderFactory.get("step1.manager")
+public Step step1Manager(JobRepository jobRepository) {
+    return new StepBuilder("step1.manager", jobRepository)
         .<String, String>partitioner("step1", partitioner())
         .step(step1())
         .gridSize(10)