Update CI configuration to use fake BackendV2

[mtreinish]

Right now the CI runs for neko (both locally and also via the bundled action) are running using the default backend, AerSimulator. This is problematic because:

1. It's using the old backend interface BackendV1 and things are moving towards BackendV2 in force now
2. It runs simulation without noise, which means our tests likely haven't been validated on noisy backends and likely won't work if you specify an alternative backend.

We should update the run configuration to optionally set the backend to one of the fake backends. The default AerBackendPlugin already supports this via backend_selection in the config file. For neko itself we should probably run with both the aer simulator and the fake backend in CI, but also expose this as an option in the action (to not potentially break any downstream users).