Update Github workflow build & run destinations, fix respective integration tests #809

Job	Run time
spm-build-test (macos-15, iphonesimulator)	2m 55s
pod-lib-lint (macos-latest, GoogleSignInSwiftSupport.podspec)	5m 16s
pod-lib-lint (macos-latest, GoogleSignIn.podspec)	2m 54s
pod-lib-lint (macos-latest, GoogleSignIn.podspec, --use-static-frameworks)	3m 45s
pod-lib-lint (macos-latest, GoogleSignInSwiftSupport.podspec, --use-static-frameworks)	3m 59s
spm-build-test (macos-15, macosx)	2m 19s
	21m 8s

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