When a shard of unit-tests.yml fails, we want the `success` job to be
maked "Failed" (not "Skipped"). That's because "Failed" blocks the PR
from merging, whereas "Skipped" does not. This change ensures that
`success` always runs to completion rather than being cancelled as soon
as a unit test shard fails or is cancelled.
From https://github.com/marketplace/actions/alls-green#options:
> Important: For this to work properly, it is a must to have the job always run,
> otherwise GitHub will make it skipped when any of the dependencies fail. In
> some contexts, skipped is interpreted as success which may lead to undersired,
> unobvious and even dangerous (as in security breach "dangerous") side-effects.
Closes https://github.com/openedx/edx-platform/issues/34789
b063dfc1ea