Add bun support #79

Job	Run time
test (ubuntu-latest, 2.7)	24s
test (ubuntu-latest, 3.0)	16s
test (ubuntu-latest, 3.1)	16s
test (ubuntu-latest, head)	14s
test (ubuntu-latest, jruby)	1m 7s
test (ubuntu-latest, jruby-head)	1m 1s
test (ubuntu-latest, truffleruby)	43s
test (ubuntu-latest, truffleruby-head)	56s
test (macos-latest, 2.7)	56s
test (macos-latest, 3.0)	23s
test (macos-latest, 3.1)	27s
test (macos-latest, head)	36s
test (macos-latest, jruby)	2m 19s
test (macos-latest, jruby-head)	1m 23s
test (macos-latest, truffleruby)	2m 4s
test (macos-latest, truffleruby-head)	2m 46s
	15m 51s

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