zeta: Fix update required notification not showing (#25588)

This PR fixes an issue introduced in #25530 that broke the notifications
that inform the user that a Zed update is required to continue using
edit prediction.

The issue is that the `Workspace` stored on the `Editor` is set _after_
the point we initialize Zeta, so capturing the `Workspace` at
construction time leads to it being `None`.

@ConradIrwin suggested that we could obtain the `Workspace` from the
`Window`, which does indeed do the trick.

I tested it both with and without this change by mocking the error
response, like so:

```rs
let response: Result<PredictEditsResponse, anyhow::Error> =
    Err(anyhow!(ZedUpdateRequiredError {
        minimum_version: SemanticVersion::new(0, 1, 0),
    }));
```

Release Notes:

- N/A

crates/zeta/src/zeta.rs

@@ -704,7 +704,10 @@ and then another
         can_collect_data: bool,
         cx: &mut Context<Self>,
     ) -> Task<Result<Option<InlineCompletion>>> {
-        let workspace = self.workspace.as_ref().and_then(|w| w.upgrade());
+        let workspace = self
+            .workspace
+            .as_ref()
+            .and_then(|workspace| workspace.upgrade());
         self.request_completion_impl(
             workspace,
             project,