[chore] Reduce port contention in service tests #28701

Job	Run time
govulncheck	38s
setup-environment	27s
lint	4m 54s
unittest-matrix (ubuntu-latest, ~1.24)	2m 23s
unittest-matrix (ubuntu-latest, ~1.23)	2m 36s
checks	2m 22s
cross-build-collector (aix, ppc64)	51s
test-coverage	8m 8s
cross-build-collector (darwin, amd64)	50s
cross-build-collector (darwin, arm64)	51s
cross-build-collector (linux, 386)	51s
cross-build-collector (linux, amd64)	58s
cross-build-collector (linux, arm64)	59s
cross-build-collector (linux, ppc64le)	49s
cross-build-collector (linux, arm, 7)	53s
cross-build-collector (linux, s390x)	49s
cross-build-collector (windows, 386)	54s
cross-build-collector (windows, amd64)	54s
unittest	1s
	31m 8s

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