ci: Bump Emacs 29.x to 3 #7

Job	Run time
test (ubuntu-latest, 26.3, false)	30s
test (ubuntu-latest, 27.2, false)	28s
test (ubuntu-latest, 28.2, false)	28s
test (ubuntu-latest, 29.3, false)	52s
test (macos-latest, 26.3, false)	1m 54s
test (macos-latest, 27.2, false)	1m 46s
test (macos-latest, 28.2, false)	2m 22s
test (macos-latest, 29.3, false)	2m 7s
test (windows-latest, 26.3, false)	1m 56s
test (windows-latest, 27.2, false)	1m 3s
test (windows-latest, 28.2, false)	44s
test (windows-latest, 29.3, false)	45s
test (ubuntu-latest, snapshot, true)	29s
test (macos-latest, snapshot, true)	1m 56s
test (windows-latest, snapshot, true)	36s
	17m 56s

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