Inconsistency between yielding Metadata and outlet_events extras for partitioned Assets

### Under which category would you file this issue? Airflow Core ### Apache Airflow version Airflow 3.2.1 ### What happened and how to reproduce it? I have a DAG that produces partitioned Assets. It contains a dynamicaly mapped task group of which one task has an Asset defined an outlet and emitts _AssetEvents_ for each expanded instance of the TaskGroup. When I used `yield Metadata` the downstream DAG was triggered by each _AssetEvent_, so one run of the source DAG could result in e.g. three _DagRuns_ of the downstream DAG. However, when I upgraded from Airflow 2.10.4 to Airflow 3.2.1, I also switched to attaching extra information to _AssetEvents_ with `outlet_events[ASSET].extra`. The first issue I encountered was that _AssetEvents_ did not show up in the UI, when `outlet_events` wasn`t a keyword only argument in the producing task function. E.g. ``` def producing_function(input: str, outlet_events=None): """Example producing task""" `outlet_events[ASSET].extra = {"section": "XY"} ``` Did not show AssetEvents. But it triggered the downstream DAG that then hang because the AssetEvent was not accessible. Making _outlet_events_ a keyword argument like this: ``` def producing_function(input: str, *, outlet_events=None): """Example producing task""" `outlet_events[ASSET].extra = {"section": "XY"} ``` produced visible _AssetEvents_. The downstream DAG gets triggered only once but shows all three _AssetEvents_ with the attached extra metadata from the three mapped taskgroup instances in the producing DAG. When I use `yield Metadata(ASSET, {"section": "XY"})` in the producing task, each _TaskInstance_ triggers a DagRun of the downstream DAG with the extra metadata properly attached (which I expected to happen and how it was before). The documentation indicates that `yield Metadata` and `outlet_events[ASSET].extra` are equivalent: https://airflow.apache.org/docs/apache-airflow/3.2.2/authoring-and-scheduling/assets.html#attaching-extra-information-to-a…