retrieval: Reduce flakiness of TestTargetManagerChan
retrieval: Reduce flakiness of TestTargetManagerChan

This will increase test time by a few hundred ms,
this is the 2nd most common cause of flakiness.

yanghongkjxy/prometheus,tomwilkie/prometheus,yanghongkjxy/prometheus,amorken/prometheus,tattsun/prometheus,SaltedMan/prometheus-annotated,kzittritsch/prometheus,Gouthamve/prometheus,trigrass2/prometheus,gottwald/prometheus,sudhi-vm/prometheus,dmilstein/prometheus,dsymonds/prometheus,amorken/prometheus,agaoglu/prometheus,GoogleCloudPlatform/prometheus,Gouthamve/prometheus,keegancsmith/prometheus,Stackdriver/stackdriver-prometheus,keegancsmith/prometheus,gottwald/prometheus,slok/prometheus,Gouthamve/prometheus,jbdalido/prometheus,Conorbro/prometheus,alileza/prometheus,alileza/prometheus,Stackdriver/stackdriver-prometheus,agaoglu/prometheus,brancz/prometheus,trigrass2/prometheus,dmilstein/prometheus,amorken/prometheus,adamron1/prometheus,gottwald/prometheus,eliothedeman/prometheus,PrFalken/prometheus,eliothedeman/prometheus,brancz/prometheus,SaltedMan/prometheus-annotated,alileza/prometheus,mtanda/prometheus,agaoglu/prometheus,Conorbro/prometheus,tomwilkie/prometheus,wrouesnel/prometheus,tattsun/prometheus,dsymonds/prometheus,AlekSi/prometheus,prometheus/prometheus,Stackdriver/stackdriver-prometheus,eliothedeman/prometheus,GoogleCloudPlatform/prometheus,gottwald/prometheus,jbdalido/prometheus,yanghongkjxy/prometheus,kangwoo/prometheus,alileza/prometheus,thachmai/prometheus,GoogleCloudPlatform/prometheus,agaoglu/prometheus,JavierZunzunegui/prometheus,Colstuwjx/prometheus,Stackdriver/stackdriver-prometheus,jbdalido/prometheus,sudhi-vm/prometheus,ton31337/prometheus,ton31337/prometheus,SaltedMan/prometheus-annotated,ton31337/prometheus,Colstuwjx/prometheus,tomwilkie/prometheus,dln/prometheus,PrFalken/prometheus,ton31337/prometheus,wrouesnel/prometheus,amorken/prometheus,mtanda/prometheus,adamron1/prometheus,SaltedMan/prometheus-annotated,wrouesnel/prometheus,yanghongkjxy/prometheus,jbdalido/prometheus,msiebuhr/prometheus,alileza/prometheus,datajet-io/prometheus,Conorbro/prometheus,GoogleCloudPlatform/prometheus,prometheus/prometheus,iksaif/prometheus,AlekSi/prometheus,slok/prometheus,trigrass2/prometheus,adamron1/prometheus,kangwoo/prometheus,dmilstein/prometheus,iksaif/prometheus,keegancsmith/prometheus,Colstuwjx/prometheus,Colstuwjx/prometheus,adamron1/prometheus,iksaif/prometheus,JavierZunzunegui/prometheus,thachmai/prometheus,wrouesnel/prometheus,datajet-io/prometheus,slok/prometheus,prometheus/prometheus,mtanda/prometheus,keegancsmith/prometheus,JavierZunzunegui/prometheus,msiebuhr/prometheus,kzittritsch/prometheus,dsymonds/prometheus,sudhi-vm/prometheus,thachmai/prometheus,GoogleCloudPlatform/prometheus,Gouthamve/prometheus,dln/prometheus,slok/prometheus,PrFalken/prometheus,datajet-io/prometheus,PrFalken/prometheus,brancz/prometheus,JavierZunzunegui/prometheus,prometheus/prometheus,kangwoo/prometheus,eliothedeman/prometheus,iksaif/prometheus,sudhi-vm/prometheus,kangwoo/prometheus,msiebuhr/prometheus,dln/prometheus,mtanda/prometheus,prometheus/prometheus,kzittritsch/prometheus,datajet-io/prometheus,tomwilkie/prometheus,kzittritsch/prometheus,tattsun/prometheus,thachmai/prometheus,brancz/prometheus,dmilstein/prometheus,msiebuhr/prometheus,trigrass2/prometheus,AlekSi/prometheus,AlekSi/prometheus,keegancsmith/prometheus,dsymonds/prometheus,dln/prometheus,tattsun/prometheus,Conorbro/prometheus