Add pending job state to default unique job states

Here, add the `pending` job state to the set of default unique states.
`pending` was a relatively recent addition in #301 and probably should
always have been in the default unique states, but `pending` isn't used
yet so no one noticed one way or the other.

internal/dbunique/db_unique_test.go

@@ -398,6 +398,7 @@ func TestUniqueInserter_JobInsert(t *testing.T) {
 		// already been done above.
 		for _, defaultState := range []rivertype.JobState{
 			rivertype.JobStateCompleted,
+			rivertype.JobStatePending,
 			rivertype.JobStateRunning,
 			rivertype.JobStateRetryable,
 			rivertype.JobStateScheduled,