message: Our current Catch2 helper says that an exception "contains" a message,
  when it was /expected/ to contain a message. This fixes the message to
  not be misleading.
diff: @@ -37,7 +37,7 @@ public:
  }
  std::string describe() const override {
  - return std::string("mongocxx::exception contains message: \"") + expected_msg + "\"";
  + return std::string("mongocxx::exception was expected to contain the message: \"") + expected_msg + "\"";
  }
  };
  } // namespace test_util
  