Fix Warning caught with Werror in CI

Author: steve-downey

examples/expected.cpp

@@ -1,4 +1,4 @@
 // examples/expected.cpp                                              -*-C++-*-
 #include <beman/expected/expected.hpp>
 
-int main(int argc, char** argv) { return 0; }
+int main(int /*argc*/, char** /*argv*/) { return 0; }