[widgets][algorithmeditor] Make migrated algorithm sequential rather than legacy

Legacy is used as a temporary state to people can
execute their algorithms using the V2 backend.

The editor does not allow to create legacy algorithm, therefore
this will trigger an update of the code directly to become what
is closer to v1 which is sequential.

beat/editor/test/test_algorithmeditor.py

@@ -105,7 +105,7 @@ class TestHelperMethods:
         assert v1_declaration != v2_declaration
         assert v2_declaration["schema_version"] == 2
         assert v2_declaration["api_version"] == 2
-        assert v2_declaration["type"] == "legacy"
+        assert v2_declaration["type"] == "sequential"
 
     @pytest.mark.parametrize(
         ["algorithm_name", "new_type", "field_to_add"],

beat/editor/widgets/algorithmeditor.py

@@ -96,7 +96,7 @@ def migrate_to_api_v2(asset):
         declaration = new_asset.declaration
         declaration["api_version"] = 2
         declaration["schema_version"] = 2
-        declaration["type"] = "legacy"
+        declaration["type"] = "sequential"
         new_asset.declaration = declaration
 
     return status, new_asset