ci: Bump Emacs 29.x to 3 #53

Job	Run time
build (ubuntu-latest, 26.3, false)	34s
build (ubuntu-latest, 27.2, false)	40s
build (ubuntu-latest, 28.2, false)	32s
build (ubuntu-latest, 29.3, false)	42s
build (macos-latest, 26.3, false)	2m 28s
build (macos-latest, 27.2, false)	1m 45s
build (macos-latest, 28.2, false)	1m 57s
build (macos-latest, 29.3, false)	1m 50s
build (windows-latest, 26.3, false)	1m 50s
build (windows-latest, 27.2, false)	1m 18s
build (windows-latest, 28.2, false)	50s
build (windows-latest, 29.3, false)	1m 13s
build (ubuntu-latest, snapshot, true)	31s
build (macos-latest, snapshot, true)	1m 55s
build (windows-latest, snapshot, true)	37s
	18m 42s

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