Shouldn't warn that deleted fiel is not part of the open workspace

[drewnoakes]

1. Use a Copilot agent and have it delete the C# file that's open in the editor

2. See a popup warning you about this:

   

   The file has been deleted, so of course it's not in the workspace:

   

We shouldn't show this toast for deleted files.

[claudiaregio]

@dibarbet Jake will talk to you about taking over his work here tomorrow