Checklist
Issue
When trying to release v2.8.7 of charm-tools in the snapstore, I noticed that there were no builds available to release into arm64, ppc64el and s390x. This means that the tools to build them will miss features, bug fixes and security updates. The 2.8 branch was made amd64 only in commit 98edcd3.
Solution
Update the snap/snapcraft.yaml to produce builds for arm64, ppc64el and s390x and get them building and into the snapstore.