Fix valgrind installation on CI #496

Job	Run time
valgrind	6m 14s
head-versions (ubuntu, jruby-head)	47s
other (ubuntu, jruby-9.4)	59s
head-versions (ubuntu, ruby-head)	27s
other (ubuntu, jruby-9.3)	42s
other (ubuntu, truffleruby)	1m 19s
mri (ubuntu-latest, 2.6)	40s
mri (ubuntu-latest, 3.1)	28s
mri (ubuntu-latest, 3.2)	40s
mri (ubuntu-latest, 3.0)	25s
mri (macos-13, 2.5)	1m 35s
mri (ubuntu-latest, 3.3)	38s
mri (ubuntu-latest, 3.4)	40s
mri (windows-latest, 2.5)	2m 13s
mri (macos-latest, 3.2)	26s
mri (windows-latest, 3.2)	2m 2s
mri (ubuntu-latest, 2.5)	1m 9s
mri (ubuntu-latest, 2.7)	34s
	21m 58s

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