A hint about the canonical issue is missing in notifications when marking an issue as duplicate
/duplicate #NNNN is closing the duplicated ticket and
cross-referencing both, which is great. However, the only notification I
get when doing that is something like
Issue was closed by Georg Koppen Issue #40028: tpo/applications/tor-browser#40028 (closed)
There is no mentioning at all about that issue a) being a duplicate and b) which ticket it is a duplicate of.
That makes it very hard for tracking tickets by looking at your inbox or even to know by reading your mail which ticket you need to keep track of instead.
Thus, either we should make sure users are getting a notification once a ticket is marked as duplicate (containing a hint about the canonical ticket) OR the closing notification should contain that information.