BUG/MEDIUM: fix missing set-var-fmt in http_after_response_rule #1032

Job	Run time
generate-specification	1m 2s
generate-models	7m 22s
HAProxy check commit message	-1s
license-check	0s
lint-spec	0s
Build	0s
go mod tidy	0s
golangci-lint	0s
Test equal	0s
Tests	0s
e2e on HAProxy	0s
	8m 23s

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