fix(arangodb): replace deprecated add_hash_index with add_persistent_index

add_hash_index() was removed in python-arango >= 8; persistent indexes
are the recommended replacement and cover the same use case.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: 2 people

tests/community/arangodb/test_arangodb.py

@@ -34,7 +34,7 @@ def arango_test_ops(arango_client, expected_version, username="root", password="
     students = database.create_collection("students")
 
     # Add a hash index to the collection.
-    students.add_hash_index(fields=["name"], unique=True)
+    students.add_persistent_index(fields=["name"], unique=True)
 
     # Insert new documents into the collection. (students_to_insert_cnt)
     students.insert({"name": "jane", "age": 39})