ci: Bump Emacs 29.x to 3 #17

Job	Run time
test (ubuntu-latest, 26.3, false)	35s
test (ubuntu-latest, 27.2, false)	28s
test (ubuntu-latest, 28.2, false)	31s
test (ubuntu-latest, 29.3, false)	34s
test (macos-latest, 26.3, false)	2m 11s
test (macos-latest, 27.2, false)	2m 12s
test (macos-latest, 28.2, false)	1m 37s
test (macos-latest, 29.3, false)	1m 51s
test (windows-latest, 26.3, false)	1m 15s
test (windows-latest, 27.2, false)	58s
test (windows-latest, 28.2, false)	43s
test (windows-latest, 29.3, false)	1m 8s
test (ubuntu-latest, snapshot, true)	27s
test (macos-latest, snapshot, true)	1m 28s
test (windows-latest, snapshot, true)	40s
	16m 38s

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