Bump peaceiris/actions-gh-pages from 3 to 4 #500

Job	Run time
test (ubuntu-latest, 27.2, false)	55s
test (ubuntu-latest, 28.2, false)	41s
test (ubuntu-latest, 29.3, false)	52s
test (macos-latest, 27.2, false)	1m 56s
test (macos-latest, 28.2, false)	2m 34s
test (macos-latest, 29.3, false)	2m 45s
test (windows-latest, 27.2, false)	1m 24s
test (windows-latest, 28.2, false)	1m 12s
test (windows-latest, 29.3, false)	1m 19s
test (ubuntu-latest, snapshot, true)	43s
test (macos-latest, snapshot, true)	2m 33s
test (windows-latest, snapshot, true)	1m 10s
	18m 4s

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