When binding has failed, `Done` gets called by
`handleBindingCycleError`. Calling it again is at best redundant and worse,
suffers from a data race:
- the `assumedPodInfo` is placed in the backoff queue
- an event causes the `Pod` pointer to get updated in it
- reading `assumedPodInfo.Pod.UID` races with that write
This race was found with`go test -race`.