Better Cross Swift Package CI

[paulb777]

Update CI involving GoogleAppMeasurement to depend on an environment variable like ProcessInfo.processInfo.environment["SWIFTCI_USE_LOCAL_DEPS"] == nil from https://github.com/apple/swift-docc/blob/5e0729b7b63f5ef39dc5b5af05e18431c86f8427/Package.swift#L107-L132 instead of a sed command.