Workflows: checking that the snap builds is only perfomed on an arm64 runner

[artiepoole]

we should be testing that the snap builds for all targeted architectures we build for in the snap store to avoid nasty surprises.
Targeted archs:

• arm64
• amd64
• ppc64el
• riscv64

[artiepoole]

Note jq snap doesn't exist in stable for riscv64...