The lockfile was last written by CocoaPods 1.16.2 while the macOS runner
ships 1.17.0, so `flutter build macos --config-only` ran pod install,
rewrote the marker, and tripped the guard that asserts Flutter
configuration leaves the committed lockfile untouched. ios/Podfile.lock
already records 1.17.0, which is why only macOS failed.
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