[Bugfix] Update dgl function `random_walk_pe` to be compatible with latest scipy (#5945)

Co-authored-by: Hongzhi (Steve), Chen <chenhongzhi.nkcs@gmail.com>

python/dgl/transforms/functional.py

@@ -22,6 +22,7 @@ from collections.abc import Iterable, Mapping
 import numpy as np
 import scipy.sparse as sparse
 import scipy.sparse.linalg
+from packaging.version import Version
 
 try:
     import torch as th
@@ -3589,7 +3590,13 @@ def random_walk_pe(g, k, eweight_name=None):
             shape=(N, N),
         )
         A = A.multiply(W)
-    RW = np.array(A / (A.sum(1) + 1e-30))  # 1-step transition probability
+    # 1-step transition probability
+    if Version(scipy.__version__) < Version("1.11.0"):
+        RW = np.array(A / (A.sum(1) + 1e-30))
+    else:
+        # Sparse matrix divided by a dense array returns a sparse matrix in
+        # scipy since 1.11.0.
+        RW = (A / (A.sum(1) + 1e-30)).toarray()
 
     # Iterate for k steps
     PE = [F.astype(F.tensor(RW.diagonal()), F.float32)]