ci: Bump Emacs 29.x to 3 #108

Job	Run time
test (ubuntu-latest, 26.3, false)	30s
test (ubuntu-latest, 27.2, false)	30s
test (ubuntu-latest, 28.2, false)	26s
test (ubuntu-latest, 29.3, false)	35s
test (macos-latest, 26.3, false)	1m 47s
test (macos-latest, 27.2, false)	1m 47s
test (macos-latest, 28.2, false)	1m 39s
test (macos-latest, 29.3, false)	2m 14s
test (windows-latest, 26.3, false)	1m 36s
test (windows-latest, 27.2, false)	1m 3s
test (windows-latest, 28.2, false)	38s
test (windows-latest, 29.3, false)	47s
test (ubuntu-latest, snapshot, true)	31s
test (macos-latest, snapshot, true)	1m 29s
test (windows-latest, snapshot, true)	38s
	16m 10s

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