fix: Message.referenced_message returns wrong data

[Damego]

About

This pull request fixes wrong serialization for Message.referenced_message attr

Checklist

• The pre-commit code linter has been run over all edited files to ensure the code is linted.
• I've ensured the change(s) work on 3.8.6 and higher.

I've made this pull request: (check all that apply)

• For the documentation
• To add a new feature
• As a general enhancement
• As a refactor of the library/the library's code
• To fix an existing bug
• To resolve #ISSUENUMBER

This is:

• A breaking change

[mAxYoLo01]

LGTM