Aluminum cans are usually only about a tenth of a millimeter or so in thickness. You need a full millimeter up but with the can you are only getting about a fifth or a quarter of a millimeter.
I don't see any 25.4>26.4 shims available for handlebars, but it is a common shim for seatposts. You could buy one of these and saw it down to size.
https://www.ebay.com/itm/Bicycle-Sea...4383.l4275.c10
The best solution is to use a 25.4mm stem.