ci: Bump Emacs 29.x to 3 #28

Job	Run time
test (ubuntu-latest, 26.3, false)	26s
test (ubuntu-latest, 27.2, false)	29s
test (ubuntu-latest, 28.2, false)	32s
test (ubuntu-latest, 29.3, false)	32s
test (macos-latest, 26.3, false)	1m 40s
test (macos-latest, 27.2, false)	2m 6s
test (macos-latest, 28.2, false)	1m 32s
test (macos-latest, 29.3, false)	1m 45s
test (windows-latest, 26.3, false)	2m 5s
test (windows-latest, 27.2, false)	54s
test (windows-latest, 28.2, false)	38s
test (windows-latest, 29.3, false)	39s
test (ubuntu-latest, snapshot, true)	24s
test (macos-latest, snapshot, true)	1m 38s
test (windows-latest, snapshot, true)	37s
	15m 57s

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