[Bug] TH 4.1.1 : Filter by "IMPORTED" does not work for alerts imported into existing cases

[H2Cyber]

Request Type

Bug

Work Environment

Question	Answer
OS version (server)	Ubuntu Server 20.04
TheHive version / git hash	4.1.1
Package Type	DEB

Steps to Reproduce

1. Merge an alert into an existing case
2. Go to the Alerts page, and filter by Imported = No. The alert above would still appear.