[mypyc] Replace deprecated _PyDict_GetItemStringWithError (python#17930)

`_PyDict_GetItemStringWithError ` was deprecated for Python 3.14 in
python/cpython#119855.
Use `PyDict_GetItemStringRef` instead. It was added in 3.13 but is
available via `pythoncapi_compat.h`.

https://docs.python.org/3/c-api/dict.html#c.PyDict_GetItemStringRef

mypyc/lib-rt/getargs.c

@@ -247,14 +247,14 @@ vgetargskeywords(PyObject *args, PyObject *kwargs, const char *format,
 #endif
         if (!skip) {
             if (i < nargs && i < max) {
-                current_arg = PyTuple_GET_ITEM(args, i);
+                current_arg = Py_NewRef(PyTuple_GET_ITEM(args, i));
             }
             else if (nkwargs && i >= pos) {
-                current_arg = _PyDict_GetItemStringWithError(kwargs, kwlist[i]);
-                if (current_arg) {
+                int res = PyDict_GetItemStringRef(kwargs, kwlist[i], &current_arg);
+                if (res == 1) {
                     --nkwargs;
                 }
-                else if (PyErr_Occurred()) {
+                else if (res == -1) {
                     return 0;
                 }
             }
@@ -265,6 +265,7 @@ vgetargskeywords(PyObject *args, PyObject *kwargs, const char *format,
             if (current_arg) {
                 PyObject **p = va_arg(*p_va, PyObject **);
                 *p = current_arg;
+                Py_DECREF(current_arg);
                 format++;
                 continue;
             }
@@ -370,8 +371,11 @@ vgetargskeywords(PyObject *args, PyObject *kwargs, const char *format,
         Py_ssize_t j;
         /* make sure there are no arguments given by name and position */
         for (i = pos; i < bound_pos_args && i < len; i++) {
-            current_arg = _PyDict_GetItemStringWithError(kwargs, kwlist[i]);
-            if (unlikely(current_arg != NULL)) {
+            int res = PyDict_GetItemStringRef(kwargs, kwlist[i], &current_arg);
+            if (res == 1) {
+                Py_DECREF(current_arg);
+            }
+            else if (unlikely(res == 0)) {
                 /* arg present in tuple and in dict */
                 PyErr_Format(PyExc_TypeError,
                              "argument for %.200s%s given by name ('%s') "
@@ -381,7 +385,7 @@ vgetargskeywords(PyObject *args, PyObject *kwargs, const char *format,
                              kwlist[i], i+1);
                 goto latefail;
             }
-            else if (unlikely(PyErr_Occurred() != NULL)) {
+            else if (unlikely(res == -1)) {
                 goto latefail;
             }
         }