Test with more modern rubies, bump runtime/development dependencies #7

Job	Run time
test (ubuntu, 2.7)	26s
test (ubuntu, 3.0)	10s
test (ubuntu, 3.1)	15s
test (ubuntu, 3.2)	14s
test (ubuntu, 3.3)	10s
test (ubuntu, truffleruby)	29s
test (ubuntu, truffleruby-head)	35s
test (macos, 2.7)	49s
test (macos, 3.0)	28s
test (macos, 3.1)	21s
test (macos, 3.2)	24s
test (macos, 3.3)	23s
test (macos, truffleruby)	1m 2s
test (macos, truffleruby-head)	1m 17s
	7m 3s

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