make clang-tidy happy

Author: dyollb

tests/test_pytypes.cpp

@@ -671,7 +671,7 @@ TEST_SUBMODULE(pytypes, m) {
 
     m.def("test_list_slicing", [](const py::list &a) { return a[py::slice(0, -1, 2)]; });
 
-    m.def("test_list_slicing_default", [](py::list a) { return a[py::slice()]; });
+    m.def("test_list_slicing_default", [](const py::list &a) { return a[py::slice()]; });
 
     // See #2361
     m.def("issue2361_str_implicit_copy_none", []() {