Fix gemspec #68

Job	Run time
test (macos-latest, 2.6)	1m 13s
test (macos-latest, 2.7)	1m 8s
test (macos-latest, 3.0)	40s
test (macos-latest, 3.1)	39s
test (macos-latest, 3.2)	36s
test (macos-latest, head)	36s
test (macos-latest, jruby)	3m 36s
test (macos-latest, jruby-head)	1m 44s
test (macos-latest, truffleruby)	1m 49s
test (macos-latest, truffleruby+graalvm)	4m 58s
test (ubuntu-20.04, 2.6)	47s
test (ubuntu-20.04, 2.7)	42s
test (ubuntu-20.04, 3.0)	19s
test (ubuntu-20.04, 3.1)	23s
test (ubuntu-20.04, 3.2)	26s
test (ubuntu-20.04, head)	25s
test (ubuntu-20.04, jruby)	1m 44s
test (ubuntu-20.04, jruby-head)	1m 32s
test (ubuntu-20.04, truffleruby)	1m 7s
test (ubuntu-20.04, truffleruby+graalvm)	2m 29s
test (windows-latest, mingw)	1m 25s
test (windows-latest, mswin)	1m 45s
test (windows-latest, jruby, true)	2m 46s
test (ubuntu-22.04, head)	18s
test (ubuntu-22.04, 3.1)	38s
test (ubuntu-22.04, 3.2)	31s
test (ubuntu-22.04, truffleruby+graalvm-head, true)	6s
test (ubuntu-22.04, truffleruby-head, true)	1m 17s
	35m 39s

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