Problem

We calculate the dbt-postgres version dependency based on the version of dbt-redshift. This causes issues when we want to keep dbt-postgres at a different version than dbt-redshift.

Solution

Treat dbt-postgres like any other dependency and simply hard code the pin.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX