Ensure RedisWrapper.items returns a list of strings

The return type of the _db.keys() is List[_StrType], where _StrType is
a str or bytes. As we want the items() method to return strings (given
the provided __getitem__ method) for keys we need an additional check.

Author: maxxiefjv

src/pyop/storage.py

@@ -155,6 +155,10 @@ def __contains__(self, key):
     def items(self):
         for key in self._db.keys(self._collection + "*"):
             visible_key = key[len(self._collection) + 1 :]
+
+            if isinstance(visible_key, bytes):
+                visible_key = visible_key.decode()
+
             try:
                 yield (visible_key, self[visible_key])
             except KeyError: