Previously `max` results stopped reading from results in tests
prematurely, as it stopped when `max` number of items were received from
the channel instead of `max` number of unique target groups received.
This caused flaky tests where the same target group was received
multiple times, as Kubernetes informers may emit the same event multiple
times.
Before this patch, running this test repeatedly failed eventually. After
this patch I have run the test many thousand times without failure.
```bash
go test -run TestEndpointsDiscoveryNamespaces -count 1000 -test.v
```
Signed-off-by: Frederic Branczyk <fbranczyk@gmail.com>