Whitelist str for skipping read-only attributes

* Fix #478 by whitelisting str for skipping read-only attrs

* Add changelog entry for str errors

* Move new fix from 3.0.3 to 3.0.4

CHANGES.rst

@@ -1,11 +1,17 @@
+v3.0.4
+======
+    * Fixed an issue with django.SafeString and other classes inheriting from
+      str having read-only attribute errors (#478) (+481)
+
 v3.0.3
 ======
     * Compatibilty with Pandas and Cython 3.0 was added. (#460) (+477)
     * Fixed a bug where pickling some built-in classes (e.g. zoneinfo) 
       could return a ``None`` module. (#447)
     * Fixed a bug where unpickling a missing class would return a different object
       instead of ``None``. (+471)
-    * Fixed the handling of missing classes when setting ``on_missing`` to ``warn`` or ``error``. (+471)
+    * Fixed the handling of missing classes when setting ``on_missing`` to ``warn``
+      or ``error``. (+471)
     * The test suite was made compatible with Python 3.12.
     * The tox configuration was updated to generate code coverage reports.
     * The suite now uses ``ruff`` to validate python code.

jsonpickle/unpickler.py

@@ -626,11 +626,11 @@ def _restore_from_dict(self, obj, instance, ignorereserved=True):
                         # i think this is the only way to set frozen dataclass attrs
                         object.__setattr__(instance, k, value)
                     except AttributeError as e:
-                        # some objects may raise this for read-only attributes (#422)
+                        # some objects may raise this for read-only attributes (#422) (#478)
                         if (
                             hasattr(instance, "__slots__")
                             and not len(instance.__slots__)
-                            and issubclass(instance.__class__, int)
+                            and issubclass(instance.__class__, (int, str))
                         ):
                             continue
                         raise e