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Add benchmarks/gc_balloon.rb #2088

Job	Run time
benchmark-ractor (head)	6m 40s
benchmark-run-once	1m 19s
benchmark-default (head)	14m 17s
benchmark-default (truffleruby, --excludes=knucleotide,lobsters,ruby-lsp,shipit)	11m 38s
test (head)	56s
benchmark-ractor-only (head)	37s
benchmark-default (ruby)	12m 3s
test (ruby)	53s
test (truffleruby)	1m 21s
benchmark-graph	1m 3s
all-tests	3s
	50m 50s