chore: Fix violations of elided_named_lifetimes (#18330)

I compile Zed from nightly build pretty often and I've noticed that
we're getting a few hits on new rustc lint:
https://github.com/rust-lang/rust/pull/129207

Release Notes:

- N/A

crates/workspace/src/workspace.rs

@@ -2119,7 +2119,7 @@ impl Workspace {
     pub fn items<'a>(
         &'a self,
         cx: &'a AppContext,
-    ) -> impl 'a + Iterator<Item = &Box<dyn ItemHandle>> {
+    ) -> impl 'a + Iterator<Item = &'a Box<dyn ItemHandle>> {
         self.panes.iter().flat_map(|pane| pane.read(cx).items())
     }