[SIEM][CASE] Incorrect dropdown selection when changing connector

[cnasikas]

If you try to change and save the external incident management system when another request is active the action fails. That's intended and is working as expected. The dropdown is not aware of the failure and selects the new external incident management system instead of the old one.

[elasticmachine]

Pinging @elastic/siem (Team:SIEM)