Handle exceptions from resumeExternalUserAgentFlowWithURL #862

Job	Run time
spm-build-test (macos-15, iphonesimulator)	4m 34s
spm-build-test (macos-15, macosx)	2m 4s
pod-lib-lint (macos-13, GoogleSignInSwiftSupport.podspec, --use-static-frameworks)	13m 45s
pod-lib-lint (macos-13, GoogleSignInSwiftSupport.podspec)	12m 9s
pod-lib-lint (macos-13, GoogleSignIn.podspec)	20m 33s
pod-lib-lint (macos-13, GoogleSignIn.podspec, --use-static-frameworks)	11m 34s
	1h 4m 39s

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