Update get_filtered_columns_in_relation to return empty list in parsing mode

[katieclaiborne-duet]

resolves #969

Problem

The documentation for dbt-audit-helper's compare and classify macros suggests using dbt_utils.get_filtered_columns_in_relation to pass in long column lists for comparison. However, doing so results in the compilation error below.

(venv) katieclaiborne@Mac dbt % dbt compile -s compare_and_classify_relation_rows -t main
19:18:48  Running with dbt=1.9.8
19:18:49  Registered adapter: bigquery=1.9.2
19:18:50  Encountered an error:
Compilation Error in analysis compare_and_classify_query_results (analyses/audit_helper/compare_and_classify_query_results.sql)
  can only concatenate list (not "str") to list
  
  > in macro compare_and_classify_query_results (macros/compare_and_classify_query_results.sql)
  > called by analysis compare_and_classify_query_results (analyses/audit_helper/compare_and_classify_query_results.sql)

Solution

As suggested in #969, I've updated the return type in parsing mode from string to list, so that the type is consistent across modes.

Checklist

• This code is associated with an issue which has been triaged and accepted for development.
• 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
• I have updated the README.md (if applicable)

[katieclaiborne-duet]

Sorry to bother, but could I ask for a review?

[katieclaiborne-duet]

Thank you, Benoit!