geo_alchemy: make application context available to db function

[mreid-tt]

Similar to #2308, this fix is needed for the app to launch

[samuelhwilliams]

I don't seem to get any errors about missing app context when running this example. Can you share your error message(s) and what versions of python libraries you're using please?

This is an inoffensive change, I just can't reproduce the issue and I'd be curious to know exactly where the problem is.

[hasansezertasan]

My traceback:

Traceback (most recent call last):
  File "C:\Users\hasansezertasan\Desktop\flask-admin\examples\geo_alchemy\app.py", line 99, in <module>
    db.create_all()
  File "C:\Users\hasansezertasan\Desktop\flask-admin\venv\Lib\site-packages\flask_sqlalchemy\extension.py", line 900, in create_all
    self._call_for_binds(bind_key, "create_all")
  File "C:\Users\hasansezertasan\Desktop\flask-admin\venv\Lib\site-packages\flask_sqlalchemy\extension.py", line 871, in _call_for_binds
    engine = self.engines[key]
             ^^^^^^^^^^^^
  File "C:\Users\hasansezertasan\Desktop\flask-admin\venv\Lib\site-packages\flask_sqlalchemy\extension.py", line 687, in engines
    app = current_app._get_current_object()  # type: ignore[attr-defined]
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\hasansezertasan\Desktop\flask-admin\venv\Lib\site-packages\werkzeug\local.py", line 519, in _get_current_object
    raise RuntimeError(unbound_message) from None
RuntimeError: Working outside of application context.

This typically means that you attempted to use functionality that needed
the current application. To solve this, set up an application context
with app.app_context(). See the documentation for more information.

[hasansezertasan]

LGTM