[UA] Shared ownership between Management and Core (#204723)

## Summary

Let's see if this time sticks

.github/CODEOWNERS

@@ -938,7 +938,7 @@ x-pack/plugins/stack_connectors @elastic/response-ops
 x-pack/plugins/task_manager @elastic/response-ops
 x-pack/plugins/telemetry_collection_xpack @elastic/kibana-core
 x-pack/plugins/triggers_actions_ui @elastic/response-ops
-x-pack/plugins/upgrade_assistant @elastic/kibana-management
+x-pack/plugins/upgrade_assistant @elastic/kibana-core
 x-pack/solutions/observability/packages/alert_details @elastic/obs-ux-management-team
 x-pack/solutions/observability/packages/alerting_test_data @elastic/obs-ux-management-team
 x-pack/solutions/observability/packages/get_padded_alert_time_range_util @elastic/obs-ux-management-team

x-pack/plugins/upgrade_assistant/kibana.jsonc

@@ -1,7 +1,9 @@
 {
   "type": "plugin",
   "id": "@kbn/upgrade-assistant-plugin",
-  "owner": "@elastic/kibana-management",
+  "owner": [
+    "@elastic/kibana-core"
+  ],
   "group": "platform",
   "visibility": "private",
   "plugin": {