Do not raise AttributeError when parsing non-string UUIDs

When a user sends a dictionary or other object as a UUID variable like `{[123]}`, previously graphene crashed with an `AttrbuteError`, like this:

```
(…)
  File "…/lib/python3.12/site-packages/graphql/utils/is_valid_value.py", line 78, in is_valid_value
    parse_result = type.parse_value(value)
                   ^^^^^^^^^^^^^^^^^^^^^^^
  File "…/lib/python3.12/site-packages/graphene/types/uuid.py", line 33, in parse_value
    return _UUID(value)
           ^^^^^^^^^^^^
  File "/usr/lib/python3.12/uuid.py", line 175, in __init__
    hex = hex.replace('urn:', '').replace('uuid:', '')
          ^^^^^^^^^^^
AttributeError: 'dict' object has no attribute 'replace'
```

But an `AttributeError` makes it seem like this is the server's fault, when it's obviously the client's.

Report a proper GraphQLError.

graphene/types/tests/test_uuid.py

@@ -36,6 +36,21 @@ def test_uuidstring_query_variable():
     assert result.data == {"uuid": uuid_value}
 
 
+def test_uuidstring_invalid_argument():
+    uuid_value = {"not": "a string"}
+
+    result = schema.execute(
+        """query Test($uuid: UUID){ uuid(input: $uuid) }""",
+        variables={"uuid": uuid_value},
+    )
+    assert result.errors
+    assert len(result.errors) == 1
+    assert (
+        result.errors[0].message
+        == "Variable '$uuid' got invalid value {'not': 'a string'}; UUID must be a string"
+    )
+
+
 def test_uuidstring_optional_uuid_input():
     """
     Test that we can provide a null value to an optional input

graphene/types/uuid.py

@@ -1,5 +1,6 @@
 from uuid import UUID as _UUID
 
+from graphql.error import GraphQLError
 from graphql.language.ast import StringValueNode
 from graphql import Undefined
 
@@ -28,4 +29,6 @@ def parse_literal(node, _variables=None):
 
     @staticmethod
     def parse_value(value):
+        if not isinstance(value, str):
+            raise GraphQLError("UUID must be a string")
         return _UUID(value)