Merge pull request #386 from msgpack/fix-valgrind-ci #497

Job	Run time
valgrind	6m 4s
other (ubuntu, jruby-9.4)	44s
other (ubuntu, jruby-9.3)	42s
head-versions (ubuntu, ruby-head)	29s
other (ubuntu, truffleruby)	1m 21s
mri (ubuntu-latest, 2.5)	29s
mri (ubuntu-latest, 3.1)	28s
mri (ubuntu-latest, 3.4)	40s
mri (ubuntu-latest, 2.7)	35s
head-versions (ubuntu, jruby-head)	54s
mri (ubuntu-latest, 3.0)	35s
mri (ubuntu-latest, 3.3)	30s
mri (windows-latest, 3.2)	1m 45s
mri (windows-latest, 2.5)	2m 46s
mri (macos-13, 2.5)	1m 27s
mri (ubuntu-latest, 3.2)	32s
mri (ubuntu-latest, 2.6)	35s
mri (macos-latest, 3.2)	30s
	21m 6s

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