ci: Bump Emacs 29.x to 3 #30

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)	33s
test (macos-latest, 26.3, false)	1m 36s
test (macos-latest, 27.2, false)	1m 31s
test (macos-latest, 28.2, false)	1m 44s
test (macos-latest, 29.3, false)	2m 7s
test (windows-latest, 26.3, false)	1m 40s
test (windows-latest, 27.2, false)	49s
test (windows-latest, 28.2, false)	41s
test (windows-latest, 29.3, false)	39s
test (ubuntu-latest, snapshot, true)	31s
test (macos-latest, snapshot, true)	2m 22s
test (windows-latest, snapshot, true)	38s
	16m 16s

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