fix: restore rp-connect-docs branch to main in local playbook (#530)

PR #523 accidentally changed the branch reference from main to
auto-docs/update-rpcn-connector-docs (a now-deleted branch).

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: mfernest

local-antora-playbook.yml

@@ -23,7 +23,7 @@ content:
     branches: main
     start_paths: [docs,'*/docs']
   - url: https://github.com/redpanda-data/rp-connect-docs
-    branches: auto-docs/update-rpcn-connector-docs
+    branches: main
 ui:
   bundle:
     url: https://github.com/redpanda-data/docs-ui/releases/latest/download/ui-bundle.zip