Fixed data race in unboundedchannel while closing #601

Job	Run time
Tests (Int) (aws-kinesis)	2m 40s
Tests (Int) (aws-sqs)	2m 25s
Tests (Unit)	1m 10s
Building, Linting, Formatting	31s
Tests (Int) (kafka)	2m 24s
Tests (PG) - PG 13 / TSDB 2.11	10m 47s
Tests (Int) (nats)	2m 8s
Tests (Int) (redis)	2m 3s
Tests (PG) - PG 13 / TSDB latest	10m 33s
Tests (Int) (redpanda)	2m 21s
Tests (Int) (http)	2m 3s
Tests (PG) - PG 14 / TSDB 2.11	11m 51s
Tests (PG) - PG 14 / TSDB latest	11m 54s
Tests (PG) - PG 15 / TSDB 2.11	11m 39s
Tests (PG) - PG 15 / TSDB latest	12m 24s
	1h 26m 53s

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