Update upgrading-users-core-version.md

Author: rishabhpoddar

v2/contribute/checklists/saas/upgrading-users-core-version.md

@@ -1054,3 +1054,6 @@ ALTER TABLE user_roles DROP CONSTRAINT IF EXISTS user_roles_role_fkey;
 ALTER TABLE totp_user_devices ADD COLUMN IF NOT EXISTS created_at BIGINT default 0;
 ALTER TABLE totp_user_devices ALTER COLUMN created_at DROP DEFAULT;
 ```
+
+### 9.0 to 9.1
+When transferring data from older / source master db to newer one, we have to modify the insert query to set `is_first_factors_null` to true when inserting into the `tenant_configs` (in the target master db).