Combine measurement and stddev columns #1729

Job	Run time
benchmark-graph	48s
test (head)	49s
benchmark-default (ruby)	14m 14s
test (ruby)	44s
benchmark-default (truffleruby, --excludes=knucleotide,lobsters,ruby-lsp,shipit)	13m 6s
benchmark-ractor-only (head)	39s
benchmark-ractor (head)	6m 45s
benchmark-run-once	1m 35s
benchmark-default (head)	12m 33s
test (truffleruby)	1m 37s
all-tests	3s
	52m 53s

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