Add tests for ARM Linux in CI

[teor2345]

We currently release ARM Linux binaries, but we don't run tests on ARM Linux.

This is a gap in our test coverage, if there is a bug specific to ARM Linux, we won't find it in CI.

How to test this

• Add ARM Linux runners to our runs-on config (also in Build ARM Linux binaries on ARM Linux machines #3668)
• Add those runners to our Rust test matrix (and maybe clippy):
  • for autonomys
  • for forks

There's not much point adding ARM Linux to other jobs, because they are unlikely to fail if clippy and tests pass.