Fix usage of undefined C-API function "_PyGen_Send" in Py3.10.

Cython/Utility/Coroutine.c

@@ -788,6 +788,32 @@ PyObject *__Pyx_Coroutine_MethodReturn(CYTHON_UNUSED PyObject* gen, PyObject *re
     return retval;
 }
 
+#if CYTHON_COMPILING_IN_CPYTHON && PY_VERSION_HEX >= 0x03030000 && (defined(__linux__) || PY_VERSION_HEX >= 0x030600B3)
+static CYTHON_INLINE
+PyObject *__Pyx_PyGen_Send(PyGenObject *gen, PyObject *arg) {
+#if PY_VERSION_HEX < 0x030A00A1
+    return _PyGen_Send(gen, arg);
+#else
+    PyObject *result;
+    // PyGen_Send() asserts non-NULL arg
+    if (PyGen_Send(gen, arg ? arg : Py_None, &result) == PYGEN_RETURN) {
+        if (PyAsyncGen_CheckExact(gen)) {
+            assert(result == Py_None);
+            PyErr_SetNone(PyExc_StopAsyncIteration);
+        }
+        else if (result == Py_None) {
+            PyErr_SetNone(PyExc_StopIteration);
+        }
+        else {
+            _PyGen_SetStopIterationValue(result);
+        }
+        Py_CLEAR(result);
+    }
+    return result;
+#endif
+}
+#endif
+
 static CYTHON_INLINE
 PyObject *__Pyx_Coroutine_FinishDelegation(__pyx_CoroutineObject *gen) {
     PyObject *ret;
@@ -829,13 +855,13 @@ static PyObject *__Pyx_Coroutine_Send(PyObject *self, PyObject *value) {
         #if CYTHON_COMPILING_IN_CPYTHON && PY_VERSION_HEX >= 0x03030000 && (defined(__linux__) || PY_VERSION_HEX >= 0x030600B3)
         // _PyGen_Send() is not exported before Py3.6
         if (PyGen_CheckExact(yf)) {
-            ret = _PyGen_Send((PyGenObject*)yf, value == Py_None ? NULL : value);
+            ret = __Pyx_PyGen_Send((PyGenObject*)yf, value == Py_None ? NULL : value);
         } else
         #endif
         #if CYTHON_COMPILING_IN_CPYTHON && PY_VERSION_HEX >= 0x03050000 && defined(PyCoro_CheckExact) && (defined(__linux__) || PY_VERSION_HEX >= 0x030600B3)
         // _PyGen_Send() is not exported before Py3.6
         if (PyCoro_CheckExact(yf)) {
-            ret = _PyGen_Send((PyGenObject*)yf, value == Py_None ? NULL : value);
+            ret = __Pyx_PyGen_Send((PyGenObject*)yf, value == Py_None ? NULL : value);
         } else
         #endif
         {
@@ -931,7 +957,7 @@ static PyObject *__Pyx_Generator_Next(PyObject *self) {
         #if CYTHON_COMPILING_IN_CPYTHON && PY_VERSION_HEX >= 0x03030000 && (defined(__linux__) || PY_VERSION_HEX >= 0x030600B3)
         // _PyGen_Send() is not exported before Py3.6
         if (PyGen_CheckExact(yf)) {
-            ret = _PyGen_Send((PyGenObject*)yf, NULL);
+            ret = __Pyx_PyGen_Send((PyGenObject*)yf, NULL);
         } else
         #endif
         #ifdef __Pyx_Coroutine_USED