[Bug] Temporary Tables not being cleaned for MERGE and on_schema_change != 'ignore'

[joshuao11]

Is this a new bug in dbt-bigquery?

• I believe this is a new bug in dbt-bigquery
• I have searched the existing issues, and I could not find an existing issue for this bug

Current Behavior

If you had some example model:

{{
    config(
        materialized='incremental',
        schema='some_example_data_set',
        alias='some_example_model',
        incremental_strategy = 'merge',
        unique_key='example_unique_key',
        on_schema_change= 'sync_all_columns',
    )
}}

When we run the model we create a temporary table (as we have specified to have it check the schema some_example_model__dbt_tmp)

Which is then used for the MERGE:

dbt-bigquery/dbt/include/bigquery/macros/materializations/incremental_strategy/merge.sql

Line 30 in 79fbd90

{% set build_sql = get_merge_sql(target_relation, source_sql, unique_key, dest_columns, predicates) %}

However we do not clean the temporary table

Expected Behavior

The temporary table is removed as part of the run, like it currently is for insert_overwrite:

dbt-bigquery/dbt/include/bigquery/macros/materializations/incremental_strategy/insert_overwrite.sql

Line 91 in 79fbd90

{%- if tmp_relation_exists -%}

Would I be able to raise a PR against main to fix this? it's not the biggest issue in the world but can make user facing datasets unnecessarily messy for 12 hours until the tables self delete

Steps To Reproduce

1. Run model
2. Observe not deleted temp tables

Relevant log output

No response

Environment

- OS:
- Python:
- dbt-core:
- dbt-bigquery: 1.8

Additional Context

No response