Update What's New for 6.0

docs/modules/ROOT/pages/whats-new.adoc

@@ -16,3 +16,4 @@ Reorganize imports
 * https://github.com/spring-projects/spring-security/issues/7349 - Move filter and token to appropriate packages
 Reorganize imports
 * https://github.com/spring-projects/spring-security/issues/11026[gh-11026] - Use `RequestAttributeSecurityContextRepository` instead of `NullSecurityContextRepository`
+* https://github.com/spring-projects/spring-security/pull/11887[gh-11827] - Change default authority for `oauth2Login()`