Sync `Py_TPFLAGS_MANAGED_DICT` for PyPy3.11 across the codebase (#5537)

* Sync `Py_TPFLAGS_MANAGED_DICT` for PyPy3.11 across the codebase

Adjust the `Py_TPFLAGS_MANAGED_DICT` logic in `include/pybind11/attr.h`
to match the one used in `include/pybind11/detail/class.h`.

This is a followup to #5508.

* Use a common `#define` for pre-`Py_TPFLAGS_MANAGED_DICT` Pythons

* style: pre-commit fixes

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

include/pybind11/attr.h

diff --git a/include/pybind11/attr.h b/include/pybind11/attr.h
index c863d8b..eb15ffd 100644
--- a/include/pybind11/attr.h
+++ b/include/pybind11/attr.h
@@ -359,7 +359,7 @@
 
         bases.append((PyObject *) base_info->type);
 
-#if PY_VERSION_HEX < 0x030B0000
+#ifdef PYBIND11_BACKWARD_COMPATIBILITY_TP_DICTOFFSET
         dynamic_attr |= base_info->type->tp_dictoffset != 0;
 #else
         dynamic_attr |= (base_info->type->tp_flags & Py_TPFLAGS_MANAGED_DICT) != 0;

include/pybind11/detail/class.h

diff --git a/include/pybind11/detail/class.h b/include/pybind11/detail/class.h
index 1ed2e90..aac6e84 100644
--- a/include/pybind11/detail/class.h
+++ b/include/pybind11/detail/class.h
@@ -574,9 +574,9 @@
 inline void enable_dynamic_attributes(PyHeapTypeObject *heap_type) {
     auto *type = &heap_type->ht_type;
     type->tp_flags |= Py_TPFLAGS_HAVE_GC;
-#if PY_VERSION_HEX < 0x030B0000 || defined(PYPY_VERSION) // For PyPy see PR #5508
-    type->tp_dictoffset = type->tp_basicsize;            // place dict at the end
-    type->tp_basicsize += (ssize_t) sizeof(PyObject *);  // and allocate enough space for it
+#ifdef PYBIND11_BACKWARD_COMPATIBILITY_TP_DICTOFFSET
+    type->tp_dictoffset = type->tp_basicsize;           // place dict at the end
+    type->tp_basicsize += (ssize_t) sizeof(PyObject *); // and allocate enough space for it
 #else
     type->tp_flags |= Py_TPFLAGS_MANAGED_DICT;
 #endif

include/pybind11/detail/common.h

diff --git a/include/pybind11/detail/common.h b/include/pybind11/detail/common.h
index 8336f8b..372dd06 100644
--- a/include/pybind11/detail/common.h
+++ b/include/pybind11/detail/common.h
@@ -1256,5 +1256,10 @@
 #    define PYBIND11_DETAILED_ERROR_MESSAGES
 #endif
 
+// CPython 3.11+ provides Py_TPFLAGS_MANAGED_DICT, but PyPy3.11 does not, see PR #5508.
+#if PY_VERSION_HEX < 0x030B0000 || defined(PYPY_VERSION)
+#    define PYBIND11_BACKWARD_COMPATIBILITY_TP_DICTOFFSET
+#endif
+
 PYBIND11_NAMESPACE_END(detail)
 PYBIND11_NAMESPACE_END(PYBIND11_NAMESPACE)