CI/CD jobs stay queued until a machine begins them

A job is now running only once one of its machine's tasks starts, and sandboxIds lists each sandbox as soon as it begins the job, not only when the job ends. While a job is queued, its reason says what it waits for (for example, "Waiting for a machine: the check's machines are starting, or running other jobs' tasks"), the console shows how long it has waited, and the check's runtime run on GitHub says how many jobs are waiting and for how long. Previously a job could report running for many minutes while its tasks waited behind other jobs' tasks.