feat: Drop Emacs 27.x #34

Job	Run time
test (ubuntu-latest, 28.2, false)	46s
test (ubuntu-latest, 29.4, false)	1m 22s
test (ubuntu-latest, 30.1, false)	1m 3s
test (macos-latest, 28.2, false)	1m 29s
test (macos-latest, 29.4, false)	1m 46s
test (macos-latest, 30.1, false)	1m 52s
test (windows-latest, 28.2, false)	1m 26s
test (windows-latest, 29.4, false)	1m 25s
test (windows-latest, 30.1, false)	3m 12s
test (ubuntu-latest, snapshot, true)	39s
test (macos-latest, snapshot, true)	1m 28s
test (windows-latest, snapshot, true)	1m 20s
	17m 48s

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