Prepare for 9.0.0 release #770

Job	Run time
pod-lib-lint (macos-13, GoogleSignIn.podspec)	12m 56s
pod-lib-lint (macos-13, GoogleSignInSwiftSupport.podspec)	9m 56s
pod-lib-lint (macos-13, GoogleSignIn.podspec, --use-static-frameworks)	29m 39s
pod-lib-lint (macos-13, GoogleSignInSwiftSupport.podspec, --use-static-frameworks)	11m 3s
spm-build-test (macos-latest, macosx)	1m 25s
spm-build-test (macos-latest, iphonesimulator)	2m 14s
	1h 7m 13s

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