CREATE SOURCE ... FROM POSTGRES CONNECTION should fail for a yugabyte connection

[def-]

What version of Materialize are you using?

main

What is the issue?

Probably also related to #29658:

> CREATE SECRET pgpass AS 'yugabyte'
> CREATE CONNECTION pg TO YUGABYTE (
    HOST yugabyte,
    PORT 5433,
    DATABASE yugabyte,
    USER yugabyte,
    PASSWORD SECRET pgpass
  )

$ postgres-execute connection=postgres://yugabyte:yugabyte@yugabyte:5433/yugabyte
ALTER USER yugabyte WITH replication;
DROP SCHEMA IF EXISTS public CASCADE;
DROP PUBLICATION IF EXISTS mz_source;
CREATE SCHEMA public;
CREATE TABLE add_columns (f1 INTEGER);
ALTER TABLE add_columns REPLICA IDENTITY FULL;
INSERT INTO add_columns VALUES (1);
CREATE TABLE remove_column (f1 INTEGER, f2 VARCHAR(2));
ALTER TABLE remove_column REPLICA IDENTITY FULL;
INSERT INTO remove_column VALUES (2, 'ab');
CREATE PUBLICATION mz_source FOR ALL TABLES;

> CREATE SOURCE mz_source
  FROM POSTGRES CONNECTION pg (PUBLICATION 'mz_source')
  FOR ALL TABLES;

Fails:

alter-table-after-source.td:109:1: error: executing query failed: db error: ERROR: POSTGRES source validation: PUBLICATION mz_source is empty: ERROR: POSTGRES source validation: PUBLICATION mz_source is empty
     |
  14 | > CREATE SECRET pgpa ... [rest of line truncated for security]
  20 |     PASSWORD SECRET  ... [rest of line truncated for security]
  23 | $ postgres-execute c ... [rest of line truncated for security]
 108 |
 109 | > CREATE SOURCE mz_source
     | ^

The mistake is that it should be YUGABYTE CONNECTION instead of POSTGRES CONNECTION:

> CREATE SOURCE mz_source
  FROM YUGABYTE CONNECTION pg (PUBLICATION 'mz_source')
  FOR ALL TABLES;

I believe we should error out and not treat the connection as a connection to postgres.