Issue #29360: _PyStack_AsDict() doesn't check kwnames

Remove two assertions which can fail on legit code. Keyword arguments are
checked later with better tests and raise a regular (TypeError) exception.
diff --git a/Objects/abstract.c b/Objects/abstract.c
index 5864032..1e394f8 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -2413,8 +2413,7 @@
     for (i = 0; i < nkwargs; i++) {
         PyObject *key = PyTuple_GET_ITEM(kwnames, i);
         PyObject *value = *values++;
-        assert(PyUnicode_CheckExact(key));
-        assert(PyDict_GetItem(kwdict, key) == NULL);
+        /* If key already exists, replace it with the new value */
         if (PyDict_SetItem(kwdict, key, value)) {
             Py_DECREF(kwdict);
             return NULL;