fix: Correctly initialize Account session in API helper

[cgumb]

Summary

Fixes a bug in src/gradescopeapi/api/api.py where the Account class was being initialized with an invalid session object.

Details

The get_account helper function was incorrectly passing the function reference get_gs_connection_session to the Account class constructor. It should have been passing the
requests.Session object returned by calling that function.

This resulted in an Account instance where self.session was a function, not a session object.
The fix is to correctly call get_gs_connection_session() to pass the expected session object during initialization.

Reference to the issue

This latent bug was discovered during the development and debugging of a new utility script that relied on the API's components.