Alembic Migrations: env.py Deprecation Warning from SQLAlchemy > 1.4.x

[pythononwheels]

Produces a warning in running tests.

migrations/env.py:62: SADeprecationWarning: Table.tometadata() is renamed to Table.to_metadata() (deprecated since: 1.4)
    t.tometadata(m)

[pythononwheels]

Adapt method call to new naming convention for SQLAlchemy > 1.4.x (aka 2.0 API)