Enable clippy::unit_arg (#8742)

This PR enables the
[`clippy::unit_arg`](https://rust-lang.github.io/rust-clippy/master/index.html#/unit_arg)
rule and suppresses the false positive that it flags.

Release Notes:

- N/A

crates/gpui/src/platform/mac/platform.rs

@@ -497,7 +497,7 @@ impl Platform for MacPlatform {
         options: WindowOptions,
     ) -> Box<dyn PlatformWindow> {
         // Clippy thinks that this evaluates to `()`, for some reason.
-        #[allow(clippy::clone_on_copy)]
+        #[allow(clippy::unit_arg, clippy::clone_on_copy)]
         let renderer_context = self.0.lock().renderer_context.clone();
         Box::new(MacWindow::open(
             handle,