ci: Bump Emacs 29.x to 3 #39

Job	Run time
test (ubuntu-latest, 26.3, false)	29s
test (ubuntu-latest, 27.2, false)	31s
test (ubuntu-latest, 28.2, false)	28s
test (ubuntu-latest, 29.3, false)	38s
test (macos-latest, 26.3, false)	1m 40s
test (macos-latest, 27.2, false)	1m 48s
test (macos-latest, 28.2, false)	1m 56s
test (macos-latest, 29.3, false)	2m 5s
test (windows-latest, 26.3, false)	1m 59s
test (windows-latest, 27.2, false)	1m 5s
test (windows-latest, 28.2, false)	47s
test (windows-latest, 29.3, false)	51s
test (ubuntu-latest, snapshot, true)	33s
test (macos-latest, snapshot, true)	1m 31s
test (windows-latest, snapshot, true)	37s
	16m 58s

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