ci: Exclude macos tests below 27.x #19

Job	Run time
build (ubuntu-latest, 26.3, false)	28s
build (ubuntu-latest, 27.2, false)	46s
build (ubuntu-latest, 28.2, false)	53s
build (ubuntu-latest, 29.3, false)	54s
build (macos-latest, 28.2, false)	1m 21s
build (macos-latest, 29.3, false)	1m 27s
build (windows-latest, 26.3, false)	5m 2s
build (windows-latest, 27.2, false)	1m 32s
build (windows-latest, 28.2, false)	1m 11s
build (windows-latest, 29.3, false)	1m 4s
build (ubuntu-latest, snapshot, true)	42s
build (macos-latest, snapshot, true)	1m 17s
build (windows-latest, snapshot, true)	35s
	17m 12s

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