fix(backup): name ansible_target_groups (kept) and email_outbox_events (left out) (#5672)

The guard in tests/core/test_backup_contents.py caught both on run 9073.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

steward/backup/contents.py

@@ -18,7 +18,7 @@ KEPT: frozenset[str] = frozenset({
     "hosts", "host_agent_registrations",
     "monitors",
     "alert_rules", "alert_states", "maintenance_windows",
-    "ansible_targets", "ansible_groups", "ansible_schedules",
+    "ansible_targets", "ansible_groups", "ansible_target_groups", "ansible_schedules",
     "dashboards", "dashboard_widgets", "dashboard_share_tokens",
     "snmp_devices", "prometheus_targets",
     # Names given to network clients by hand (UniFi's alias column).
@@ -31,7 +31,7 @@ KEPT: frozenset[str] = frozenset({
 EXCLUDED: frozenset[str] = frozenset({
     "plugin_metrics", "plugin_metric_latest", "plugin_metrics_hourly",
     "monitor_results",
-    "email_outbox", "password_resets",
+    "email_outbox", "email_outbox_events", "password_resets",
     # Run history; its logs live on disk, not in the database.
     "ansible_runs",
     "docker_containers", "docker_disk_usage", "docker_events", "docker_host_status",