Tests

Bump up version to 3.1.0 #62

Job	Run time
test (ubuntu-latest, head)	11s
test (ubuntu-latest, 3.3)	9s
test (ubuntu-latest, 3.2)	12s
test (ubuntu-latest, 3.1)	12s
test (ubuntu-latest, 3.0)	9s
test (ubuntu-latest, jruby)	39s
test (ubuntu-latest, jruby-head)	38s
test (ubuntu-latest, truffleruby)	32s
test (ubuntu-latest, truffleruby-head)	31s
test (ubuntu-latest, truffleruby+graalvm)	1m 37s
test (windows-latest, head)	1m 9s
test (windows-latest, 3.3)	2m 24s
test (windows-latest, mingw)	59s
test (windows-latest, mswin)	1m 14s
test (windows-latest, ucrt)	1m 48s
test (macos-latest, head)	20s
test (macos-latest, 3.3)	21s
	13m 5s

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