ci: enable merge groups for auto-merge-dependabot workflow

Adds merge_group trigger to the auto-merge-dependabot workflow to enable
automated PR rebasing through GitHub's merge queue feature, reducing manual
intervention during the merge process.

This change aligns with the equivalent update from microsoft/kiota PR #6952.

Signed-off-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: ramsessanchez

.github/workflows/auto-merge-dependabot.yml

@@ -3,6 +3,7 @@ name: Auto-merge dependabot updates
 on:
   pull_request:
     branches: [ main ]
+  merge_group:
 
 permissions:
   pull-requests: write