fix(pep0249): Use the wrapped value in CTX instead of unwrapped

[Ferenc-]

No description provided.

[pvital]

LGTM

I tested it in two different ways, with a Flask app connecting to a PostgreSQL server. The first test was using the built-in Flask web server [1], and the second one was with uWSGI [2]. Both tests used the following code, and they worked, as you can see in [1] and [2].

    with get_db_connection() as conn:
        with conn.cursor() as cur:
            cur.execute(
                'SELECT * from Users;'
            )
            users = cur.fetchall()

[1] https://instana.rocks/s/-h9kZcw7RqunpU_WibydYQ
[2] https://instana.rocks/s/hfmukSbUSDqJ3t1kfUNCRg