Use the macos-12 runner. #212

Job	Run time
pod-lib-lint	3m 45s
pod-lib-lint (--use-libraries)	5m 7s
spm-build-test	56s
pod-lib-lint (--use-static-frameworks)	3m 26s
xcode-project-test (-scheme AppAuth-iOS -destination 'platform=iOS Simulator,name=iPhone 11,OS=16...	3m 15s
xcode-project-test (-scheme AppAuth-macOS -destination 'platform=macOS,arch=x86_64' -sdk 'macosx1...	41s
xcode-project-test (-scheme AppAuth_macOS -destination 'platform=macOS,arch=x86_64' -sdk 'macosx1...	31s
xcode-project-test (-scheme AppAuth-tvOS -destination 'platform=tvOS Simulator,name=Apple TV,OS=1...	1m 47s
xcode-project-test (-scheme AppAuth_tvOS -destination 'platform=tvOS Simulator,name=Apple TV,OS=1...	1m 37s
xcode-project-test (-scheme AppAuthTV -destination 'platform=tvOS Simulator,name=Apple TV,OS=16.1...	1m 8s
	22m 13s

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