ci: Exclude macos tests below 27.x #39

Job	Run time
test (ubuntu-latest, 26.3, false)	38s
test (ubuntu-latest, 27.2, false)	42s
test (ubuntu-latest, 28.2, false)	37s
test (ubuntu-latest, 29.3, false)	48s
test (macos-latest, 28.2, false)	1m 24s
test (macos-latest, 29.3, false)	1m 33s
test (windows-latest, 26.3, false)	3m 53s
test (windows-latest, 27.2, false)	1m 56s
test (windows-latest, 28.2, false)	1m 35s
test (windows-latest, 29.3, false)	1m 25s
test (ubuntu-latest, snapshot, true)	32s
test (macos-latest, snapshot, true)	1m 21s
test (windows-latest, snapshot, true)	33s
	16m 57s

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