ci: Bump Emacs 29.x to 3 #50

Job	Run time
test (ubuntu-latest, 26.3, false)	28s
test (ubuntu-latest, 27.2, false)	30s
test (ubuntu-latest, 28.2, false)	28s
test (ubuntu-latest, 29.3, false)	39s
test (macos-latest, 26.3, false)	1m 46s
test (macos-latest, 27.2, false)	1m 58s
test (macos-latest, 28.2, false)	1m 34s
test (macos-latest, 29.3, false)	1m 51s
test (windows-latest, 26.3, false)	1m 38s
test (windows-latest, 27.2, false)	1m 0s
test (windows-latest, 28.2, false)	40s
test (windows-latest, 29.3, false)	49s
test (ubuntu-latest, snapshot, true)	29s
test (macos-latest, snapshot, true)	1m 30s
test (windows-latest, snapshot, true)	39s
	15m 59s

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