fix(ci): upgrade macOS runners from macos-14 to macos-26 #3157

Job	Run time
test / test-dart-vm (3.9.0)	1m 36s
test / test-dart-vm (stable)	1m 37s
native_test / test-dart-native (windows-latest)	2m 32s
ddc_test / test-dart-ddc (stable, firefox)	1m 57s
ddc_test / test-dart-ddc (stable, chrome)	1m 54s
ddc_test / test-dart-ddc (3.9.0, chrome)	2m 4s
dart2js_test / test-dart-2js (3.9.0, chrome)	1m 50s
dart2js_test / test-dart-2js (stable, chrome)	1m 42s
native_test / test-dart-native (macos-26)	1m 48s
ddc_test / test-dart-ddc (3.9.0, firefox)	2m 6s
dart2js_test / test-dart-2js (3.9.0, firefox)	1m 49s
dart2js_test / test-dart-2js (stable, firefox)	1m 52s
	22m 47s

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