ALTER TABLE statement cannot add GEOMETRY column

# Summary

Creating tables with geometry types is possible. Adding geometry columns to an existing table is not, at least not using the `ALTER TABLE` statement.

# Reproducible example
This was the smallest example I could come up with that demonstrates this behavior.

```sql
INSTALL spatial;
LOAD spatial;

BEGIN TRANSACTION;
CREATE TABLE t1(id VARCHAR, pt VARCHAR);
CREATE TABLE t2(id VARCHAR, geom GEOMETRY);
COMMIT;

BEGIN TRANSACTION;
ALTER TABLE t1 ADD COLUMN geom GEOMETRY;
COMMIT;

--undo
BEGIN TRANSACTION;
DROP TABLE IF EXISTS t1;
DROP TABLE IF EXISTS t2;
COMMIT;

-- verify that the geometry type is in the catalog:
SELECT COUNT(*) AS res_count FROM duckdb_types() WHERE type_name = 'GEOMETRY';

```

This results in a catalog error:
```
> Catalog Error: Type with name "GEOMETRY" is not in the catalog, but it exists in the spatial extension.
Please try installing and loading the spatial extension: INSTALL spatial; LOAD spatial;
```

If the line with the `ALTER TABLE` statement is commented out, the above SQL will execute successfully, returning the expected value for `res_count`: 1.

# Environment

DuckDB 0.9.2 on Windows 10, executing DuckDB SQL against an in-memory DB via the JDBC driver. I have not yet attempted to reproduce the issue in other environments.