Consider Removing psql type specifiers when Comparing Computed Constructs

Describe the bug
I am using a Computed column in a Postgresql database and created a migration. The next migration I create with automigration returns a warning: alembic\autogenerate\compare.py:1034: UserWarning: Computed default on table.search_vector cannot be modified

The string generated for comparison by _normalize_computed_default:
setweightto_tsvectorenglish,title,a
setweightto_tsvectorenglish::regconfig,title::text,a::char

The code responsible for this:

https://github.com/sqlalchemy/alembic/blob/44965f05e91ee5d424d9dde6566650c1bf26b516/alembic/autogenerate/compare.py#L979-L986

Proposed solution
Remove groups of text starting with :: by adding another regex substitution.

 def _normalize_computed_default(sqltext: str) -> str: 
     """we want to warn if a computed sql expression has changed.  however 
     we don't want false positives and the warning is not that critical. 
     so filter out most forms of variability from the SQL text. 
     """ 
  
    normalized_sqltext = re.sub(r"[ \(\)'\"`\[\]]", "", sqltext).lower()
    return re.sub(r"::\w+", "", normalized_sqltext)

Start in alembic/autogenerate/compare.py at _normalize_computed_default, which currently normalizes computed SQL text before comparison. Verify the PostgreSQL example, update the normalization so :: type specifiers are ignored, and confirm that equivalent computed expressions no longer produce the modification warning.