Allow test suite to run if, for example, the C++20 builds are failing but C++11 are fine.
`os_name` in include section needs to be explicit (putting it at the end doesn't apply to the extra jobs). Move macOS test to extra job instead of doing all gcc/clang (which isn't setup for mac anyway). Also adds name to build-yosys task.
Also rename `build-artifact` to use `matrix.os` for compatibility with testing across OS.