text: Title: Attribute type change in Mapped[] not detected
  Body: **Describe the bug**
  <!-- A clear and concise description of what the bug is. -->
  If I change the type of an attribute in my model, only defined by the `Mapped` annotation, then I do not get any changes in the resulting upgrade script:
  
  ```python
  class File(Base):
  
      # change type from str to int
      # size: Mapped[Optional[str]]   
      size: Mapped[Optional[int]]  
  ```
  
  ```bash
  alembic revision -m "Change not detected"  --autogenerate
  ```
  
  Not expected:
  
  ```python
  def upgrade():
      # ### commands auto generated by Alembic - please adjust! ###
      pass
      # ### end Alembic commands ###
  ```
  
  **Expected behavior**
  <!-- A clear and concise description of what you expected to happen. -->
  I expect an alter_column statement a la:
  ```python
  def upgrade():
      # ### commands auto generated by Alembic - please adjust! ###
      op.alter_column('file', 'size',
                 existing_type=sa.NUMERIC(),
                 nullable=True)
      # ### end Alembic commands ###
  ```
  
  **To Reproduce**
  I am very aware that this may be a problem on my side, and I think it is difficult to provide a complete example setup.
  
  **Versions.**
   - OS: Windows 11
   - Python: 3.10.11
   - Alembic: 1.11.1
   - SQLAlchemy: 2.0.15
   - Database: postgis/postgis:11-2.5-alpine 
   - DBAPI: psycopg2-binary 2.9.6
  
  **Additional context**
  <!-- Add any other context about the problem here. -->
  Doing other changes to my model class, for instance, removing the `Optional` keyword or adding/removing/renaming, results in an expected change (except still no type change).
  
  **Have a nice day!**
  