🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

Author: gcf-owl-bot[bot]

google/cloud/spanner_admin_database_v1/types/spanner_database_admin.py

@@ -570,6 +570,10 @@ class UpdateDatabaseDdlRequest(proto.Message):
 
             For more details, see protobuffer `self
             description <https://developers.google.com/protocol-buffers/docs/techniques#self-description>`__.
+        throughput_mode (bool):
+            Optional. This field is exposed to be used by the Spanner
+            Migration Tool. For more details, see
+            `SMT <https://github.com/GoogleCloudPlatform/spanner-migration-tool>`__.
     """
 
     database: str = proto.Field(
@@ -588,6 +592,10 @@ class UpdateDatabaseDdlRequest(proto.Message):
         proto.BYTES,
         number=4,
     )
+    throughput_mode: bool = proto.Field(
+        proto.BOOL,
+        number=5,
+    )
 
 
 class DdlStatementActionInfo(proto.Message):