[Task] Apply cleanups recommended by gemini-code-assist to the vertex task store

[gaborfeher]

We are postponing this work, because the vertex task store currently lives on two branches simultenously: 1.0-dev and main. Once 1.0-dev will be promoted to main, it will be easier to do these cleanups, and we won't risk merge conflicts between the two branches.

1. Use list comprehensions in _get_artifacts_change_event
2. Use f-string formatting in _update
3. Don't catch the broad Exception type in fake_vertex_client.py