Add verbose flag to plugin_dependencies_test to debug flake (#118755)

Author: jmagman

dev/devicelab/bin/tasks/plugin_dependencies_test.dart

@@ -284,6 +284,7 @@ public class DummyPluginAClass {
             options: <String>[
               'ios',
               '--no-codesign',
+              '--verbose',
             ],
           );
         });