fix: Use DROP + CREATE for MV partition_by changes (#1327)

CREATE OR REPLACE MATERIALIZED VIEW cannot change partition_by, so use
DROP + CREATE when partition_by is changing. This restores the previous
behavior for partition_by changes while keeping CREATE OR REPLACE for
other full refresh scenarios.

### Checklist

- [x] I have run this code in development and it appears to resolve the
stated issue
- [x] This PR includes tests, or tests are not required/relevant for
this PR
- [ ] I have updated the `CHANGELOG.md` and added information about my
change to the "dbt-databricks next" section.

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: benc-db

dbt/include/databricks/macros/relations/materialized_view/alter.sql

@@ -27,7 +27,13 @@
 ) %}
     -- apply a full refresh immediately if needed
     {% if configuration_changes.requires_full_refresh %}
-        {% do return(get_replace_sql(existing_relation, relation,  sql)) %}
+        {#- CREATE OR REPLACE cannot change partition_by, so use DROP + CREATE when partition_by changes -#}
+        {% if configuration_changes.changes["partition_by"] %}
+            {{- log('Applying REPLACE to: ' ~ existing_relation) -}}
+            {% do return(drop_and_create(existing_relation, relation, sql)) %}
+        {% else %}
+            {% do return(get_replace_sql(existing_relation, relation, sql)) %}
+        {% endif %}
 
     -- otherwise apply individual changes as needed
     {% else %}