ci: Bump Emacs 29.x to 3 #28

Job	Run time
test (ubuntu-latest, 26.3, false)	30s
test (ubuntu-latest, 27.2, false)	29s
test (ubuntu-latest, 28.2, false)	30s
test (ubuntu-latest, 29.3, false)	38s
test (macos-latest, 26.3, false)	1m 37s
test (macos-latest, 27.2, false)	2m 20s
test (macos-latest, 28.2, false)	1m 37s
test (macos-latest, 29.3, false)	1m 42s
test (windows-latest, 26.3, false)	3m 4s
test (windows-latest, 27.2, false)	1m 7s
test (windows-latest, 28.2, false)	42s
test (windows-latest, 29.3, false)	45s
test (ubuntu-latest, snapshot, true)	27s
test (macos-latest, snapshot, true)	1m 36s
test (windows-latest, snapshot, true)	35s
	17m 39s

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