Set up CI to build against a Yocto SDK

[tronical]

We have a few quirks and customisation points to enable building against Yocto SDKs. It would be good if those could get test coverage.

Building the Yocto SDK itself in GH actions might be too hard, but perhaps a smaller SDK could be built by hand and uploaded somewhere, so that a GH action here could

1. Download the SDK
2. Extract & install it
3. Perform a Rust and/or CMake build against it

Once this works, this approach could also be use in some of our dependencies that have quirks, such as the Rust Skia bindings.