assistant_context_editor: Try to fix crash when trying to view patch (#25572)

Closes #24571

Attempts to fix crash described in #24571 based on the panic trace
provided by the user. In short, the panic seemed to be caused by
attempting to read an `Entity<ContextEditor>` while it was being
updated. My assumption is that at some point in
`workspace.add_item_to_current_pane` the `ContextEditor` is read.
Therefore, I moved the workspace update outside of the ContextEditor
update, and replaced another `update` call with a `read` call to clean
it up and just in case that was actually the issue.

Release Notes:

- N/A