ci: Bump Emacs 29.x to 3 #57

Job	Run time
test (ubuntu-latest, 26.3, false)	29s
test (ubuntu-latest, 27.2, false)	28s
test (ubuntu-latest, 28.2, false)	28s
test (ubuntu-latest, 29.3, false)	40s
test (macos-latest, 26.3, false)	1m 58s
test (macos-latest, 27.2, false)	1m 42s
test (macos-latest, 28.2, false)	1m 38s
test (macos-latest, 29.3, false)	2m 6s
test (windows-latest, 26.3, false)	1m 26s
test (windows-latest, 27.2, false)	2m 4s
test (windows-latest, 28.2, false)	1m 2s
test (windows-latest, 29.3, false)	51s
test (ubuntu-latest, snapshot, true)	28s
test (macos-latest, snapshot, true)	1m 32s
test (windows-latest, snapshot, true)	34s
	17m 26s

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