Fix a bug in serviceaccount admission introduced when we switched
everything to use shared informers. That change accidentally reused the
list of secrets instead of creating a new one, resulting in all secrets
in the namespace being returned as possible service account tokens,
instead of limiting it only to the actual service account tokens, as it
did before the shared informer conversion. This also adds a unit test to
ensure there is no future regression here.
9f95cf7b4f