Fix email migration (#809)

### Description

Please explain the changes you made here.

### Checklist

- [ ] Created tests which fail without the change (if possible)
- [ ] All tests passing
- [ ] Extended the documentation, if necessary

Co-authored-by: Maxime Lemonnier <[email protected]>

Author: Rotheem

app/core/users/endpoints_users.py

@@ -704,7 +704,10 @@ async def migrate_mail(
         email=mail_migration.new_email,
         db=db,
     )
-    if user.school_id is not SchoolType.no_school and user.school_id != new_school_id:
+    if (
+        user.school_id is not SchoolType.no_school.value
+        and user.school_id != new_school_id
+    ):
         raise HTTPException(
             status_code=400,
             detail="New email address is not compatible with the current school",