BUILD/MINOR: e2e: remove unsupported versions from testing #638

Job	Run time
generate-specification	44s
HAProxy check commit message	0s
generate-models	1m 6s
license-check	15s
golangci-lint	56s
lint-spec	9s
Build	22s
go mod tidy	5s
Tests	2m 47s
e2e on HAProxy (2.1)	44s
e2e on HAProxy (2.2)	46s
e2e on HAProxy (2.3)	45s
e2e on HAProxy (2.4)	46s
e2e on HAProxy (2.5)	45s
e2e on HAProxy (2.6)	43s
e2e on HAProxy (2.7)	44s
e2e on HAProxy (2.8)	47s
	12m 24s

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