fix: _PyThreadState_GetDict(tstate) API gets removed in Python 3.13

Author: Xmader

src/PyEventLoop.cc

@@ -143,9 +143,13 @@ PyEventLoop PyEventLoop::_getLoopOnThread(PyThreadState *tstate) {
 
   #if PY_VERSION_HEX >= 0x030d0000 // Python version is greater than 3.13
   // The private `_PyThreadState_GetDict(tstate)` API gets removed in Python 3.13.
-  // However, the fix below cannot be a perfect replacement since the public `PyThreadState_GetDict()` API can only get from the current thread.
+  // However, simply replacing it with `PyThreadState_GetDict()` does not work,
+  //   since the public `PyThreadState_GetDict()` API can only get from the current thread.
   // We need to somehow get the thread dictionary on the main thread instead of the current thread.
-  PyObject *ts_dict = PyThreadState_GetDict();
+  if (tstate == NULL) {
+    return _loopNotFound();
+  }
+  PyObject *ts_dict = tstate->dict;
   #elif PY_VERSION_HEX >= 0x03090000 // Python version is greater than 3.9
   PyObject *ts_dict = _PyThreadState_GetDict(tstate);  // borrowed reference
   #else // Python 3.8