Update supported branches in workflow file

Signed-off-by: Rob Winch <362503+rwinch@users.noreply.github.com>

Author: rwinch

.github/workflows/update-antora-ui-spring.yml

@@ -16,7 +16,7 @@ jobs:
     name: Update on Supported Branches
     strategy:
       matrix:
-        branch: [ '5.8.x', '6.2.x', '6.3.x', 'main' ]
+        branch: [ '6.4.x', '6.5.x', 'main' ]
     steps:
       - uses: spring-io/spring-doc-actions/update-antora-spring-ui@e28269199d1d27975cf7f65e16d6095c555b3cd0
         name: Update