Fix software update not installing latest Big Sur update

What does this MR do?

Fixes https://gitlab.com/gitlab-org/ci-cd/shared-runners/images/macstadium/orka/-/jobs/1508281353

Why was this MR needed?

The latest Big Sur update only actually installs automatically if --restart is passed. It doesn't install when we restart ourselves, even though it gets downloaded.

I also switch to install all updates, since that is what we're checking in the specs.

What's the best way to test this MR?

What are the relevant issue numbers?