Workflow updates to support IAM user auth testing and new variables

[mikealfare]

Problem

The IAM User auth testing requires more environment variables and an updated workflow. CI uses the workflow on main for PRs, so it's difficult to test both the changes and the workflow updates.

Solution

This PR is limited to the workflow updates. Once merged, we can test the dependent PR.

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.