Add bun support #86

Job	Run time
test (ubuntu-latest, 2.7)	28s
test (ubuntu-latest, 3.0)	16s
test (ubuntu-latest, 3.1)	11s
test (ubuntu-latest, head)	18s
test (ubuntu-latest, jruby)	1m 0s
test (ubuntu-latest, jruby-head)	1m 19s
test (ubuntu-latest, truffleruby)	53s
test (ubuntu-latest, truffleruby-head)	1m 50s
test (macos-latest, 2.7)	54s
test (macos-latest, 3.0)	29s
test (macos-latest, 3.1)	20s
test (macos-latest, head)	22s
test (macos-latest, jruby)	1m 50s
test (macos-latest, jruby-head)	1m 25s
test (macos-latest, truffleruby)	1m 20s
test (macos-latest, truffleruby-head)	3m 58s
	16m 53s

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