ci: Bump Emacs 29.x to 3 #34

Job	Run time
test (ubuntu-latest, 26.3, false)	28s
test (ubuntu-latest, 27.2, false)	31s
test (ubuntu-latest, 28.2, false)	27s
test (ubuntu-latest, 29.3, false)	32s
test (macos-latest, 26.3, false)	2m 22s
test (macos-latest, 27.2, false)	2m 18s
test (macos-latest, 28.2, false)	2m 20s
test (macos-latest, 29.3, false)	1m 58s
test (windows-latest, 26.3, false)	2m 21s
test (windows-latest, 27.2, false)	55s
test (windows-latest, 28.2, false)	45s
test (windows-latest, 29.3, false)	1m 16s
test (ubuntu-latest, snapshot, true)	26s
test (macos-latest, snapshot, true)	1m 36s
test (windows-latest, snapshot, true)	46s
	19m 1s

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