Fix snapshot_check_all_get_existing_columns: use adapter.get_columns_in_relation

[jtcohen6]

#5223 caused failing tests overnight in dbt-spark + dbt-databricks

The code was written to use the get_columns_in_relation macro, rather than the get_columns_in_relation adapter method (Python). We should aim for consistency between these—but elsewhere in dbt-core, we do call it as adapter.get_columns_in_relation, so we should do the same here.

Here's the breakdown:

• For most "SQL adapters," the adapter method just redirects to the macro (SQL): source
• In dbt-bigquery, the macro redirects to the adapter method, since all the actual logic is in Python (no SQL involved): source
• In dbt-spark, the logic is written in both Python and SQL. The adapter method calls the macro, but it also does some of its own post-processing, which is missed if you just call the macro directly. I'll open a follow-up PR to rework this for consistency, but the change in this PR should be sufficient to get tests passing again.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have signed the CLA
• 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 opened an issue to add/update docs, or docs changes are not required/relevant for this PR
• I have run changie new to create a changelog entry

[jtcohen6]

PR to check whether this fixes the failing tests in CI: dbt-labs/dbt-spark#353

[McKnight-42]

Looks reasonable to me, great catch!

[dbeatty10]

Looks good to me.

Can affirm that this is the only aberrant instance -- all other materializations within the global project are currently using adapter.get_columns_in_relation

[ueshin]

I confirmed the integration tests pass now. Thanks for the quick fix!