ci: Test Emacs 29.4 #20

Job	Run time
build (ubuntu-latest, 26.3, false)	33s
build (ubuntu-latest, 27.2, false)	51s
build (ubuntu-latest, 28.2, false)	56s
build (ubuntu-latest, 29.4, false)	1m 3s
build (macos-latest, 28.2, false)	1m 34s
build (macos-latest, 29.4, false)	1m 38s
build (windows-latest, 26.3, false)	1m 21s
build (windows-latest, 27.2, false)	1m 35s
build (windows-latest, 28.2, false)	1m 10s
build (windows-latest, 29.4, false)	1m 37s
build (ubuntu-latest, snapshot, true)	44s
build (macos-latest, snapshot, true)	1m 26s
build (windows-latest, snapshot, true)	1m 5s
	15m 33s

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