[Docstring] Update a link to SQLAlchemy documentation to be compatible with 2.0 
While reading that docstring I found that the link to SQLAlchemy documentation was outdated. I propose to change it to link to a documentation of SQLAlchemy version that is actually supported (>=2.0).

Quick search in repo for string `https://docs.sqlalchemy.org/en/13` yields just that single string to be outdated.

Cheers,
Damian
thanks @heavelock 