Applying clang-tidy suggested fixes.

Author: rwgk

tests/test_pickling.cpp

@@ -37,13 +37,13 @@ void wrap(py::module m) {
         .def(py::init<>())
         .def_readwrite("num", &SimpleBase::num)
         .def(py::pickle(
-            [](py::object self) {
+            [](const py::object& self) {
                 py::dict d;
                 if (py::hasattr(self, "__dict__"))
                     d = self.attr("__dict__");
                 return py::make_tuple(self.attr("num"), d);
             },
-            [](py::tuple t) {
+            [](const py::tuple& t) {
                 if (t.size() != 2)
                     throw std::runtime_error("Invalid state!");
                 auto cpp_state = std::unique_ptr<SimpleBase>(new SimpleBaseTrampoline);