Preserve branch name for predictable rendered links in PRs

Add preserve-branch-name: true to create-pull-request safe output
so the branch name matches what the agent specifies, enabling the
rendered markdown link in the PR body to work correctly.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: felickz

.github/workflows/update-ghas-matrix.lock.yml

@@ -19,6 +19,7 @@ network:
 safe-outputs:
   create-pull-request:
     max: 1
+    preserve-branch-name: true
 ---
 
 # Update GHAS-on-GHES Feature Matrix