Return False when failed to migrate table (#2982)

Return `False` when failed to migrate.

src/databricks/labs/ucx/hive_metastore/table_migrate.py

@@ -145,7 +145,7 @@ def _migrate_managed_table(self, managed_table_external_storage: str, src_table:
         if managed_table_external_storage == 'CLONE':
             return self._migrate_table_create_ctas(src_table.src, src_table.rule)
         logger.warning(f"failed-to-migrate: unknown managed_table_external_storage: {managed_table_external_storage}")
-        return True
+        return False
 
     def _safe_migrate_table(
         self,

src/databricks/labs/ucx/hive_metastore/table_migration_status.py

@@ -119,7 +119,8 @@ def is_migrated(self, schema: str, table: str) -> bool:
                 return True
             logger.info(f"{schema}.{table} is set as not migrated")
         except NotFound:
-            # If the source table doesn't exist, it will not be shown as migrated
+            # If the source table doesn't exist anymore, we mark it as migrated to avoid trying to migrate it again and
+            # for views that have the table as dependency
             logger.warning(f"failed-to-migrate: {schema}.{table} set as a source does no longer exist")
             return True
         return False