flowey: revive ability to run CI pipelines locally

[damanm24]

The ability to iterate on CI pipelines entirely locally allows rapid testing and validation of pipeline logic without needing to rely on remote CI runs. Currently, this ability has regressed. Creating this issue to track reviving this ability of Flowey. Currently when running cargo xflowey ci checkin-gates --config ci, I am met with the following output:

Error: flowey_lib_hvlite::_jobs::test_local_flowey_build_igvm emitted GitHub YAML. Fix the node by checking `ctx.backend()` appropriately

I suspect there will be other issues that are hidden as the pipeline carries forward.