fix: add referencedSchema to PostgresQueryRunner

[JasonMan34]

Description of change

Right now, when using PostgreSQL, relations that point to tables in a different schema will have their foreign constraints generated every migration, even if they already exist.
This is because when checking for the constraint's target, referencedSchema is used to prefix the column name(s). However, in PostgresQueryRunner, referencedSchema is never set, so the query runner thinks the existing constraint is pointing to public schema, even if it isn't

This PR adds referencedSchema to the PostgresQueryRunner loading of foreign keys.

Fixes #8565

Pull-Request Checklist

• Code is up-to-date with the master branch
• npm run lint passes with this change
• npm run test passes with this change
• This pull request links relevant issues as Fixes #0000
• There are new or updated unit tests validating the change N/A
• Documentation has been updated to reflect this change N/A
• The new commits follow conventions explained in CONTRIBUTING.md

I didn't know what tests to add as there were no existing tests regarding referencedSchema
Also I don't believe this exists in the documentation

[JasonMan34]

The tests that failed are not related to do the PR.
Seems to be a problem with issue-863.ts

[AlexMesser]

thank you for contribution!