Fix an issue with node get (#3628)

Author: kddejong

src/cfnlint/decode/node.py

@@ -73,8 +73,6 @@ def __deepcopy__(self, memo):
 
         def get(self, key, default=None):
             """Override the default get"""
-            if not isinstance(key, str):
-                raise ValueError(f"Key {key!r} must be a string")
             if isinstance(default, dict):
                 default = dict_node(default, self.start_mark, self.end_mark)
             return super().get(key, default)