Return early from concurrency() and rate_limit() without limit names #15842

Job	Run time
docker, python:3.9	18s
docker, python:3.10	17s
docker, python:3.11	19s
docker, python:3.12	1m 31s
Server Tests - python:3.9, postgres:14	14s
Server Tests - python:3.10, postgres:14	27s
Server Tests - python:3.11, postgres:14	25s
Server Tests - python:3.12, postgres:14	11s
Server Tests - python:3.9, sqlite	14s
Server Tests - python:3.10, sqlite	12s
Server Tests - python:3.11, sqlite	11s
Server Tests - python:3.12, sqlite	10s
Client Tests - python:3.9, postgres:14	21s
Client Tests - python:3.10, postgres:14	28s
Client Tests - python:3.11, postgres:14	22s
Client Tests - python:3.12, postgres:14	24s
	6m 4s

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