feat: Drop Emacs 27.x #608

Job	Run time
test (ubuntu-latest, 28.2, false)	1m 10s
test (ubuntu-latest, 29.4, false)	1m 21s
test (ubuntu-latest, 30.1, false)	1m 4s
test (macos-latest, 28.2, false)	1m 59s
test (macos-latest, 29.4, false)	2m 7s
test (macos-latest, 30.1, false)	1m 53s
test (windows-latest, 28.2, false)	1m 41s
test (windows-latest, 29.4, false)	1m 51s
test (windows-latest, 30.1, false)	1m 59s
test (ubuntu-latest, snapshot, true)	53s
test (macos-latest, snapshot, true)	1m 36s
test (windows-latest, snapshot, true)	3m 5s
	20m 39s

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