Simplify borrowed-ref comments to focus on the why

Author: gpshead

Modules/_json.c

@@ -1745,10 +1745,8 @@ _encoder_iterate_mapping_lock_held(PyEncoderObject *s, PyUnicodeWriter *writer,
     PyObject *key, *value;
     for (Py_ssize_t  i = 0; i < PyList_GET_SIZE(items); i++) {
         PyObject *item = PyList_GET_ITEM(items, i);
-        // gh-142831: item is a borrowed ref from the items list.
-        // encoder_encode_key_value() may invoke user Python code
-        // (the key encoder) that can mutate or clear the list,
-        // so we must hold a strong reference.
+        // gh-142831: encoder_encode_key_value() can invoke user code
+        // that mutates the items list, invalidating this borrowed ref.
         Py_INCREF(item);
         if (!PyTuple_Check(item) || PyTuple_GET_SIZE(item) != 2) {
             PyErr_SetString(PyExc_ValueError, "items must return 2-tuples");
@@ -1779,10 +1777,8 @@ _encoder_iterate_dict_lock_held(PyEncoderObject *s, PyUnicodeWriter *writer,
     PyObject *key, *value;
     Py_ssize_t pos = 0;
     while (PyDict_Next(dct, &pos, &key, &value)) {
-        // gh-119438, gh-145244: key and value are borrowed refs from
-        // PyDict_Next(). encoder_encode_key_value() may invoke user
-        // Python code (the 'default' callback) that can mutate or
-        // clear the dict, so we must hold strong references.
+        // gh-145244: encoder_encode_key_value() can invoke user code
+        // that mutates the dict, invalidating these borrowed refs.
         Py_INCREF(key);
         Py_INCREF(value);
         if (encoder_encode_key_value(s, writer, first, dct, key, value,
@@ -1897,10 +1893,8 @@ _encoder_iterate_fast_seq_lock_held(PyEncoderObject *s, PyUnicodeWriter *writer,
 {
     for (Py_ssize_t i = 0; i < PySequence_Fast_GET_SIZE(s_fast); i++) {
         PyObject *obj = PySequence_Fast_GET_ITEM(s_fast, i);
-        // gh-142831: obj is a borrowed ref from the sequence.
-        // encoder_listencode_obj() may invoke user Python code
-        // (the 'default' callback) that can mutate or clear the
-        // sequence, so we must hold a strong reference.
+        // gh-142831: encoder_listencode_obj() can invoke user code
+        // that mutates the sequence, invalidating this borrowed ref.
         Py_INCREF(obj);
         if (i) {
             if (PyUnicodeWriter_WriteStr(writer, separator) < 0) {