[chore] change the way we unmarshal the config in tests #18365

Job	Run time
govulncheck	31s
setup-environment	7s
checks	2m 5s
lint	3m 18s
test-coverage	4m 52s
unittest-matrix (~1.22)	6m 27s
unittest-matrix (~1.21.8)	3m 44s
cross-build-collector (darwin, amd64)	44s
cross-build-collector (darwin, arm64)	36s
cross-build-collector (linux, 386)	35s
cross-build-collector (linux, amd64)	53s
cross-build-collector (linux, arm64)	42s
cross-build-collector (linux, ppc64le)	43s
cross-build-collector (linux, arm, 7)	45s
cross-build-collector (linux, s390x)	40s
cross-build-collector (windows, 386)	42s
cross-build-collector (windows, amd64)	48s
unittest	1s
	28m 13s

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