Add security-updates group to dependabot.yml (#677)

Agent-Logs-Url: https://github.com/glen-cheney/Shuffle/sessions/d9a1d43a-a0d6-4939-9fe1-fd9b5202685f

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: glen-cheney <963921+glen-cheney@users.noreply.github.com>

Author: Copilot

.github/dependabot.yml

@@ -11,3 +11,8 @@ updates:
         update-types:
           - 'minor'
           - 'patch'
+      security-updates:
+        applies-to: security-updates
+        update-types:
+          - 'minor'
+          - 'patch'