Drop support for Python 3.8

[mikealfare]

Problem

Python 3.8 reached end of life on 10/7/2024.

Solution

Drop support for Python 3.8. Update tests to no longer run on Python 3.8.

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.

[mikealfare]

The tests are all messed up due to the change in testing matrix and the fact that they run off of main. This will be merged and verified. The resulting integration tests from this merge:
https://github.com/dbt-labs/dbt-redshift/actions/runs/11391275819