Temporarily ignore MANAGED HMS tables on external storage location (#2837)

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Resolves #2838 

### Functionality

- [ ] modified existing workflow: `...`

### Tests
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describe any other relevant tests -->

- [ ] added unit tests
- [ ] added integration tests
- [ ] verified on staging environment (screenshot attached)

Author: HariGS-DB

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

@@ -179,6 +179,12 @@ def _sql_migrate_view(self, src_view: ViewToMigrate) -> str:
         return src_view.sql_migrate_view(self.index())
 
     def _migrate_external_table(self, src_table: Table, rule: Rule):
+        if src_table.object_type == "MANAGED":
+            logger.warning(
+                f"failed-to-migrate: Detected MANAGED table {src_table.name} on external storage, not currently "
+                f"supported by UCX"
+            )
+            return False
         target_table_key = rule.as_uc_table_key
         table_migrate_sql = src_table.sql_migrate_external(target_table_key)
         logger.debug(f"Migrating external table {src_table.key} to using SQL query: {table_migrate_sql}")

tests/unit/hive_metastore/test_table_migrate.py

@@ -70,7 +70,7 @@ def test_migrate_dbfs_root_tables_should_produce_proper_queries(ws):
     )
     assert (
         "SYNC TABLE `ucx_default`.`db1_dst`.`managed_mnt` FROM `hive_metastore`.`db1_src`.`managed_mnt`;"
-        in backend.queries
+        not in backend.queries
     )
     assert (
         "ALTER TABLE `hive_metastore`.`db1_src`.`managed_dbfs` "
@@ -83,7 +83,7 @@ def test_migrate_dbfs_root_tables_should_produce_proper_queries(ws):
     ) in backend.queries
     assert (
         "SYNC TABLE `ucx_default`.`db1_dst`.`managed_other` FROM `hive_metastore`.`db1_src`.`managed_other`;"
-        in backend.queries
+        not in backend.queries
     )
     migrate_grants.apply.assert_called()