fix: shorebird init will fail if gradle invocations require arguments

[eseidel]

My understanding is that sometimes customers have gradle set up so that app:tasks might require arguments to exit cleanly?

https://discord.com/channels/1030243211995791380/1318421477544169472/1318421477544169472

shorebird/packages/shorebird_cli/lib/src/executables/gradlew.dart

Line 144 in 19ef47b

Future<Set<String>> productFlavors(String projectRoot) async {