fix(tests): derive head revision in the migration round-trip test

The round-trip test builds its catalog from the models (which already
carry the head schema), then stamps the revision that was newest when the
test was written and replays everything above it. Any migration landing
on top therefore ran its DDL against a schema it had not rolled back -
the new computes.auto_connect migration failed with "duplicate column
name: auto_connect".

Stamp the current head instead and let the downgrade roll back every
revision above the inventory one before the upgrade replays them.

tests/services/test_image_reconciliation.py

@@ -401,6 +401,7 @@ async def test_path_matching_does_not_interpret_sql_wildcards(inventory, config)
 async def test_migration_roundtrip_preserves_rows_and_relationships(inventory, config):
     from alembic import command
     from alembic.config import Config
+    from alembic.script import ScriptDirectory
 
     image_file(config)
     await scan(inventory)
@@ -414,7 +415,12 @@ async def test_migration_roundtrip_preserves_rows_and_relationships(inventory, c
         cfg = Config()
         cfg.set_main_option("script_location", "gns3server:db_migrations")
         cfg.attributes["connection"] = connection
-        command.stamp(cfg, "d9e8a2b7c401")
+        # The catalog is built from the models, so it already carries the head
+        # schema. Stamping head (not the revision that happened to be newest when
+        # this test was written) keeps the round-trip valid for later migrations:
+        # every revision above the inventory one is rolled back before it is
+        # replayed, instead of being applied on top of its own schema.
+        command.stamp(cfg, ScriptDirectory.from_config(cfg).get_current_head())
         command.downgrade(cfg, "c7e4a9f1d2b6")
         assert connection.execute(text("SELECT count(*) FROM image_template_map")).scalar_one() == 1
         assert connection.execute(text("SELECT image_id FROM images")).scalar_one() == original["image_id"]