Start building against Spring Batch 5.0.3 snapshots

See gh-36833

spring-boot-project/spring-boot-dependencies/build.gradle

@@ -1341,7 +1341,7 @@ bom {
 			]
 		}
 	}
-	library("Spring Batch", "5.0.2") {
+	library("Spring Batch", "5.0.3-SNAPSHOT") {
 		group("org.springframework.batch") {
 			imports = [
 				"spring-batch-bom"