Incorrect type annotation for the result of `to_json` in `DataClassORJSONMixin`

[Fatal1ty]

• mashumaro version: 3.13
• Python version: 3.13
• Operating System: macOS Sonoma

Description

The to_json method should return str instead of bytes.

• https://github.com/Fatal1ty/mashumaro/blob/bffc024fc175d3146b521036a79d02348f846cd2/mashumaro/mixins/orjson.pyi#L27-L33