ci: Bump Emacs 29.x to 3 #38

Job	Run time
test (ubuntu-latest, 26.3, false)	41s
test (ubuntu-latest, 27.2, false)	38s
test (ubuntu-latest, 28.2, false)	36s
test (ubuntu-latest, 29.3, false)	41s
test (macos-latest, 26.3, false)	1m 47s
test (macos-latest, 27.2, false)	1m 49s
test (macos-latest, 28.2, false)	2m 6s
test (macos-latest, 29.3, false)	2m 3s
test (windows-latest, 26.3, false)	1m 54s
test (windows-latest, 27.2, false)	1m 11s
test (windows-latest, 28.2, false)	1m 3s
test (windows-latest, 29.3, false)	58s
test (ubuntu-latest, snapshot, true)	33s
test (macos-latest, snapshot, true)	2m 22s
test (windows-latest, snapshot, true)	43s
	19m 5s

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