Resolve clang-tidy errors

```
/__w/pybind11/pybind11/tests/test_callbacks.cpp:33:9: error: 'auto rec' can be declared as 'auto *rec' [readability-qualified-auto,-warnings-as-errors]
   33 |         auto rec = c.get_pointer<py::detail::function_record>();
      |         ^~~~
      |         auto *
/__w/pybind11/pybind11/tests/test_callbacks.cpp:41:13: error: 'auto cap' can be declared as 'auto *cap' [readability-qualified-auto,-warnings-as-errors]
   41 |             auto cap = reinterpret_cast<capture *>(&rec->data);
      |             ^~~~
      |             auto *
```

Author: rwgk

tests/test_callbacks.cpp

@@ -30,15 +30,15 @@ double apply_custom_transform(const py::object &src, double value) {
     if (auto cfunc = func.cpp_function()) {
         auto c = py::reinterpret_borrow<py::capsule>(PyCFunction_GET_SELF(cfunc.ptr()));
 
-        auto rec = c.get_pointer<py::detail::function_record>();
+        auto *rec = c.get_pointer<py::detail::function_record>();
 
         if (rec && rec->is_stateless
             && py::detail::same_type(typeid(raw_t *),
                                      *reinterpret_cast<const std::type_info *>(rec->data[1]))) {
             struct capture {
                 raw_t *f;
             };
-            auto cap = reinterpret_cast<capture *>(&rec->data);
+            auto *cap = reinterpret_cast<capture *>(&rec->data);
             return (*cap->f)(value);
         }
         return -200;