fix: gnu plot multiple variables #65

Job	Run time
build	17s
benchmark (big, nginx_graphql)	1m 3s
benchmark (big, tailcall_default)	53s
benchmark (big, tailcall_full_conf)	53s
benchmark (big, wundergraph_no_opt)	55s
benchmark (big, wundergraph_default)	53s
benchmark (big, apollo_router)	57s
benchmark (big, grafbase_default)	57s
benchmark (big, grafbase_cache)	1m 0s
benchmark (medium, nginx_graphql)	55s
benchmark (medium, tailcall_default)	1m 0s
benchmark (medium, tailcall_full_conf)	56s
benchmark (medium, wundergraph_no_opt)	56s
benchmark (medium, wundergraph_default)	55s
benchmark (medium, apollo_router)	57s
benchmark (medium, grafbase_default)	54s
benchmark (medium, grafbase_cache)	1m 0s
benchmark (small, nginx_graphql)	1m 1s
benchmark (small, tailcall_default)	1m 1s
benchmark (small, tailcall_full_conf)	1m 0s
benchmark (small, wundergraph_no_opt)	55s
benchmark (small, wundergraph_default)	58s
benchmark (small, apollo_router)	55s
benchmark (small, grafbase_default)	1m 0s
benchmark (small, grafbase_cache)	56s
read	7s
analyze	36s
	23m 50s

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