ci: Exclude macos tests below 27.x #6

Job	Run time
test (ubuntu-latest, 26.3, false)	38s
test (ubuntu-latest, 27.2, false)	36s
test (ubuntu-latest, 28.2, false)	38s
test (ubuntu-latest, 29.3, false)	46s
test (macos-latest, 28.2, false)	1m 18s
test (macos-latest, 29.3, false)	1m 30s
test (windows-latest, 26.3, false)	2m 31s
test (windows-latest, 27.2, false)	1m 20s
test (windows-latest, 28.2, false)	1m 2s
test (windows-latest, 29.3, false)	1m 17s
test (ubuntu-latest, snapshot, true)	35s
test (macos-latest, snapshot, true)	1m 16s
test (windows-latest, snapshot, true)	58s
	14m 25s

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