Update Github workflow build & run destinations, fix respective integration tests #812

Job	Run time
spm-build-test (macos-15, iphonesimulator)	6h 0m 22s
pod-lib-lint (macos-latest, GoogleSignIn.podspec)	5m 57s
spm-build-test (macos-15, macosx)	1m 31s
pod-lib-lint (macos-latest, GoogleSignIn.podspec, --use-static-frameworks)	5m 56s
pod-lib-lint (macos-latest, GoogleSignInSwiftSupport.podspec)	6m 15s
pod-lib-lint (macos-latest, GoogleSignInSwiftSupport.podspec, --use-static-frameworks)	5m 56s
	6h 25m 57s

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