Enable clippy::useless_conversion (#8767)

This PR enables the
[`clippy::useless_conversion`](https://rust-lang.github.io/rust-clippy/master/index.html#/useless_conversion)
rule and fixes the outstanding violations.

Release Notes:

- N/A

crates/workspace/src/dock.rs

@@ -221,7 +221,7 @@ impl Dock {
                     return;
                 };
                 if panel.is_zoomed(cx) {
-                    workspace.zoomed = Some(panel.to_any().downgrade().into());
+                    workspace.zoomed = Some(panel.to_any().downgrade());
                     workspace.zoomed_position = Some(position);
                 } else {
                     workspace.zoomed = None;