radv/ci: merge the zink jobs into one, and add testing on VanGogh
Since GL CTS, GLES CTS, and Piglit executions are very fast compared to the machine setup time, it makes sense to combine them into one boot. The execution will run until the first test suite fails, or we are done with the execution.
With this done, adding Zink testing on VanGogh was easy, so I went with it!