Start building against Spring WS 3.1.5 snapshots

See gh-33789

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

@@ -1800,7 +1800,7 @@ bom {
 			]
 		}
 	}
-	library("Spring WS", "3.1.4") {
+	library("Spring WS", "3.1.5-SNAPSHOT") {
 		prohibit("[4.0.0-M1,)") {
 			because "it uses Spring Framework 6"
 		}