Remove errant reference to structlog

[twm]

Fix an apparent copy/paste error in a deprecation warning.

I spotted this in the warnings Warehouse's tests emit:

...
tests/unit/accounts/test_services.py::TestDatabaseUserService::test_get_recovery_codes
tests/unit/accounts/test_services.py::TestDatabaseUserService::test_create_login_success
  /opt/warehouse/lib/python3.12/site-packages/passlib/handlers/argon2.py:716: DeprecationWarning: Accessing argon2.__version__ is deprecated and will be removed in a future release. Use importlib.metadata directly to query for structlog's packaging metadata.
    _argon2_cffi.__version__, max_version)
...

[hynek]

Ooops, thanks!