Add since version in javadoc

Issue: gh-4130

web/src/main/java/org/springframework/security/web/savedrequest/HttpSessionRequestCache.java

@@ -138,6 +138,7 @@ public class HttpSessionRequestCache implements RequestCache {
 	 * "SPRING_SECURITY_SAVED_REQUEST".
 	 *
 	 * @param sessionAttrName a new session attribute name.
+	 * @since 4.2.1
 	 */
 	public void setSessionAttrName(String sessionAttrName) {
 		this.sessionAttrName = sessionAttrName;