fix: Improve perf on schema enumeration/validation (#1168)

Resolves #1166 

<!---
Include the number of the issue addressed by this PR above if
applicable.

  Example:
    resolves #1234

Please review our pull request review process in CONTRIBUTING.md before
your proceed.
-->

### Description

Apparently we've had a performance regression for a while due to
switching to GetSchemas over using show schemas for everything. Prior to
1.9, you could get the show schema behavior if you were on HMS but
didn't specify a database. Unclear why GetSchema's performance is poor,
but even in my non-HMS testing, show schemas is faster.

### 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
- [x] I have updated the `CHANGELOG.md` and added information about my
change to the "dbt-databricks next" section.

Author: benc-db

CHANGELOG.md

@@ -6,6 +6,10 @@
 - Remove external path on intermediate tables for incremental models (with Materialization V2) ([1161](https://github.com/databricks/dbt-databricks/pull/1161))
 - Fix get_columns_in_relation branching logic for streaming tables to prevent it from running `AS JSON`
 
+### Under the hood
+
+- Improve performance of schema enumeration/validation ([1168](https://github.com/databricks/dbt-databricks/pull/1168))
+
 ## dbt-databricks 1.10.10 (August 20, 2025)
 
 ### Fixes

dbt/adapters/databricks/impl.py

@@ -300,21 +300,14 @@ def compare_dbr_version(self, major: int, minor: int) -> int:
         return self.connections.compare_dbr_version(major, minor)
 
     def list_schemas(self, database: Optional[str]) -> list[str]:
-        """
-        Get a list of existing schemas in database.
-
-        If `database` is `None`, fallback to executing `show databases` because
-        `list_schemas` tries to collect schemas from all catalogs when `database` is `None`.
-        """
-        if database is not None:
-            results = self.connections.list_schemas(database=database)
-        else:
-            results = self.execute_macro(LIST_SCHEMAS_MACRO_NAME, kwargs={"database": database})
+        results = self.execute_macro(LIST_SCHEMAS_MACRO_NAME, kwargs={"database": database})
         return [row[0] for row in results]
 
     def check_schema_exists(self, database: Optional[str], schema: str) -> bool:
         """Check if a schema exists."""
-        return schema.lower() in set(s.lower() for s in self.list_schemas(database=database))
+        return schema.lower() in set(
+            s.lower() for s in self.connections.list_schemas(database or "hive_metastore", schema)
+        )
 
     def execute(
         self,