Remove 1.8.latest core reference from install.

[VersusFacit]

Problem

 syntax error at or near "'foreign_key_model'" in context "key references ref('foreign_key_model'", at line 9, column 52
  compiled Code at target/run/test/models/my_model.sql

This is related to a similar snowflake issue https://github.com/dbt-labs/dbt-snowflake/pull/1150/files

Solution

Get rid of the branch reference.

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

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the dbt-redshift contributing guide.

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the dbt-redshift contributing guide.