原因はNetwork.frameworkがビルドされたコンパイラと、手元のコンパイラ（Xcode 13 beta 2) が違うことっぽい

Failed to build module 'Network'; this SDK is not supported by the compiler (the SDK is built with 'Apple Swift version 5.5 (swiftlang-1300.0.20.4 clang-1300.0.21.1)', while this compiler is 'Apple Swift version 5.5 (swiftlang-1300.0.20.104 clang-1300.0.21.1)'). Please select a toolchain which matches the SDK.