Update macOS runner to macos-15 to fix deprecation #977

Job	Run time
grab-pr-body	2s
app-check-api-token-tests	3m 7s
check-pr-body-for-key	2s
swift-button-functional-test	30s
grab-pr-body	2s
swift-button-functional-test	16m 25s
check-pr-body-for-key	2s
app-check-api-token-tests	3m 7s
app-check-api-token-tests	3m 7s
swift-button-functional-test	8m 55s
grab-pr-body	2s
check-pr-body-for-key	2s
	35m 23s

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