* Use newly published action: `diddlesnaps/snapcraft-multiarch-action`
* Upload every push to master to the Snap Store's Edge channel
* Upload every tagged prerelease to the Snap Store's Beta channel
(including release candidates which are also handled below)
* Upload every tagged stable or release candidate release to the Snap
Store's Candidate Channel
Signed-off-by: Daniel Llewellyn <daniel@snapcraft.ninja>