Add (deep)copy support to read only dict (#118204)

tests/util/test_read_only_dict.py

@@ -1,5 +1,6 @@
 """Test read only dictionary."""
 
+import copy
 import json
 
 import pytest
@@ -35,3 +36,5 @@ def test_read_only_dict() -> None:
     assert isinstance(data, dict)
     assert dict(data) == {"hello": "world"}
     assert json.dumps(data) == json.dumps({"hello": "world"})
+
+    assert copy.deepcopy(data) == {"hello": "world"}