implement autogen for PK constraints

Describe the bug
Given the following class:

class PersistedJobPartitionFile(Base):
    __tablename__ = "job_partition_files"

    job_id = Column(UUID(as_uuid=True), primary_key=True)
    partition_key = Column(String, primary_key=True)

    file_type = Column(SqlEnum(JobFileType), nullable=False, primary_key=True)

    path = Column(String, nullable=False)

I did migrations as normal, generating this line:
sa.PrimaryKeyConstraint('job_id', 'partition_key', 'file_type')

Then, I expanded the PK to include the path column:

class PersistedJobPartitionFile(Base):
    __tablename__ = "job_partition_files"

    job_id = Column(UUID(as_uuid=True), primary_key=True)
    partition_key = Column(String, primary_key=True)

    file_type = Column(SqlEnum(JobFileType), nullable=False, primary_key=True)

    # some partitions can have multiple files :/
    # so add the path to the PK
    path = Column(String, nullable=False, primary_key=True)

When autogenerating a migration, it simply creates an empty migration

Expected behavior
I expected an alter statement to be generated to adjust the PK.

Versions.

• OS: OS x
• Python: 3.7.9
• Alembic: 1.7.6
• SQLAlchemy: 1.4.31
• Database: Postgres 14
• DBAPI: psycopg2