add 6.x branches to build

antora-playbook.yml

@@ -15,7 +15,7 @@ git:
 content:
   sources:
   - url: https://github.com/spring-projects/spring-security
-    branches: [main, '5.{{6..9},{1..9}+({0..9})}.x']
+    branches: [main, '5.{{6..9},{1..9}+({0..9})}.x', '6.+({0..9}).x']
     tags: ['5.{{6..9},{1..9}+({0..9})}.+({0..9})?(-RC+({0..9}))', '6.+({0..9}).+({0..9})?(-{RC,M}*)']
     start_path: docs
 asciidoc: