rewrite abspath(__file__) to __file__ in py39+

[MarcoGorelli]

resolves #576

[asottile]

[adamantike]

I will try to create a simple example and open a separate issue, but this change is breaking a script we are running with Python 3.9 and alembic.

We run alembic upgrade --sql head, while having a line like this in alembic/env.py:

sys.path.append(os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__)))))

That works, but after running pyupgrade, that line gets replaced with:

sys.path.append(os.path.dirname(os.path.dirname(os.path.dirname(__file__))))

And the alembic command fails. Printing __file__ shows:

ipdb> __file__
'alembic/env.py'
ipdb> import sys; sys.version
'3.9.13 (main, Aug  2 2022, 11:20:39) \n[GCC 10.2.1 20210110]'