chore: add comment about version assignment (#5239)

modules/core/04-channel/keeper/upgrade.go

@@ -280,7 +280,8 @@ func (k Keeper) ChanUpgradeAck(
 
 	// optimistically accept version that TRY chain proposes and pass this to callback for confirmation
 	// in the crossing hello case, we do not modify version that our TRY call returned and instead enforce
-	// that both TRY calls returned the same version
+	// that both TRY calls returned the same version. It is possible that this will fail in the OnChanUpgradeAck
+	// callback if the version is invalid.
 	if channel.IsOpen() {
 		upgrade.Fields.Version = counterpartyUpgrade.Fields.Version
 	}