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add justfile #2070

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Run time

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Job	Run time
Build	37s
Test (2.3)	58s
Test (2.4)	59s
Test (2.5)	1m 0s
Test (2.6)	55s
Test (2.7)	55s
Test (3.0)	52s
Test (3.1)	53s
Test (3.2)	50s
Test (3.3)	55s
Test (jruby-9.4.0.0)	1m 44s
Test (truffleruby-head)	2m 28s
Publish	0s
	13m 6s