Update dbapi method to import_dbapi for APSWGSheetsDialect to remove warning at the start of program

[AndrewFucher]

Is your feature request related to a problem? Please describe.
For newer versions of SQLAlchemy (2.0), usage of dbapi() class method is deprecated. It is recommended to implement import_dbapi() class method. Docs
So, the following warning is shown every time I use SQLAlchemy with Google Sheets adapter:

SADeprecationWarning: The dbapi() class method on dialect classes has been renamed to import_dbapi().  Implement an import_dbapi() class method directly on class <class 'shillelagh.backends.apsw.dialects.gsheets.APSWGSheetsDialect'> to remove this warning; the old .dbapi() class method may be maintained for backward compatibility.

Describe the solution you'd like
I would like to update the base class APSWDialect. Remove (if it does not break anything, I am not sure how it really works rn) or extend the class with the class method import_dbapi.

Describe alternatives you've considered
Leaving as it is for now. But as it is deprecated, better follow the docs.

Additional context
Python 3.11
SQLAlchemy==2.0.20
importlib-metadata==6.8.0 (without it SQLAlchemy, ORM to be exact, does not work)

[betodealmeida]

@AndrewFucher do you want to write a PR? All you need to do is add:

import_dbapi = dbapi

Here:

shillelagh/src/shillelagh/backends/apsw/dialects/base.py

Line 61 in cd2c6b1

[betodealmeida]

Added in #452.