ci: Bump Emacs 29.x to 3 #24

Job	Run time
test (ubuntu-latest, 26.3, false)	29s
test (ubuntu-latest, 27.2, false)	29s
test (ubuntu-latest, 28.2, false)	28s
test (ubuntu-latest, 29.3, false)	32s
test (macos-latest, 26.3, false)	1m 40s
test (macos-latest, 27.2, false)	1m 34s
test (macos-latest, 28.2, false)	1m 50s
test (macos-latest, 29.3, false)	1m 58s
test (windows-latest, 26.3, false)	2m 17s
test (windows-latest, 27.2, false)	59s
test (windows-latest, 28.2, false)	37s
test (windows-latest, 29.3, false)	38s
test (ubuntu-latest, snapshot, true)	27s
test (macos-latest, snapshot, true)	1m 29s
test (windows-latest, snapshot, true)	33s
	16m 0s

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