TEST/MINOR: make acme-vars serialization testing more reliable #999

Job	Run time
generate-models	1m 43s
generate-specification	1m 8s
HAProxy check commit message	0s
Build	32s
go mod tidy	16s
license-check	42s
lint-spec	14s
golangci-lint	1m 14s
Test equal	1m 22s
Tests	56s
e2e on HAProxy (2.3)	52s
e2e on HAProxy (2.1)	52s
e2e on HAProxy (2.2)	55s
e2e on HAProxy (2.4)	54s
e2e on HAProxy (2.5)	52s
e2e on HAProxy (2.6)	56s
e2e on HAProxy (2.7)	56s
e2e on HAProxy (2.8)	56s
	15m 20s

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