[Redshift] Add tests for unit testing

[MichelleArk]

addresses: dbt-labs/dbt-core#9467
docs dbt-labs/docs.getdbt.com/#

Problem

Currently, the unit testing framework in core uses the safe_cast utils macro to convert a user-provided value for an input mock to the appropriate type. In some instances, this safe_cast may fail and need special handling depending on the type.

The acceptance criteria for this issue is to introduce a test that provides coverage across all primative input types (and arrays & objects if possible!) for unit testing input data, potentially updating the safe_cast macro as necessary.

Solution

• tests for primative types + json.
• arrays don't work out of the box and will be addressed in follow-up work.
• skipping changelog as this change just adds tests

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.