ManyToMany incorrectly triggers a ModelDefinitionError

[pmdevita]

Describe the bug
Declaring a ManyToMany error always raises a ModelDefinitionError

To Reproduce

import sqlalchemy
import databases
import ormar

DATABASE_URL = "sqlite:///test.sqlite"

ormar_config = ormar.OrmarConfig(
    metadata=sqlalchemy.MetaData(),
    database=databases.Database(DATABASE_URL),
    engine=sqlalchemy.create_engine(DATABASE_URL)
)


class Author(ormar.Model):
    ormar_config = ormar_config.copy(tablename="authors")

    id = ormar.Integer(primary_key=True)
    name = ormar.String(max_length=100)


class Book(ormar.Model):
    ormar_config = ormar_config.copy(tablename="books")

    id = ormar.Integer(primary_key=True)
    title = ormar.String(max_length=100)
    author = ormar.ManyToMany(Author)
    year = ormar.Integer(nullable=True)


ormar_config.metadata.create_all(ormar_config.engine)

running this should produce this error

ormar.exceptions.ModelDefinitionError: Relation with related_name 'author' leading to model BookAuthor cannot be used on model Book because it's already used by model Author

Expected behavior
The ManyToMany field should be created and usable.

Versions (please complete the following information):

• Database: SQLite
• Python version: 3.11
• ormar version: 0.20.1
• pydantic version: 2.5.3
• if applicable fastapi version