[MLIR] Fix thread safety of the deleter in PyDenseResourceElementsAttribute (#124832)

In general, `PyDenseResourceElementsAttribute` can get deleted at any
time and any thread, where unlike the `getFromBuffer` call, the Python
interpreter may not be initialized and the GIL may not be held.

This PR fixes segfaults caused by `PyBuffer_Release` when the GIL is not
being held by the thread calling the deleter.

Author: Fabian Tschopp

mlir/lib/Bindings/Python/IRAttributes.cpp

@@ -1468,7 +1468,10 @@ class PyDenseResourceElementsAttribute
     // The userData is a Py_buffer* that the deleter owns.
     auto deleter = [](void *userData, const void *data, size_t size,
                       size_t align) {
+      if (!Py_IsInitialized())
+        Py_Initialize();
       Py_buffer *ownedView = static_cast<Py_buffer *>(userData);
+      nb::gil_scoped_acquire gil;
       PyBuffer_Release(ownedView);
       delete ownedView;
     };