Rust 1.78 (#11314)

Notable things I've had to fix due to 1.78:
- Better detection of unused items
- New clippy lint (`assigning_clones`) that points out places where assignment operations with clone rhs could be replaced with more performant `clone_into`
Release Notes:

- N/A

crates/collab_ui/src/notifications/incoming_call_notification.rs

@@ -55,11 +55,6 @@ pub fn init(app_state: &Arc<AppState>, cx: &mut AppContext) {
     .detach();
 }
 
-#[derive(Clone, PartialEq)]
-struct RespondToCall {
-    accept: bool,
-}
-
 struct IncomingCallNotificationState {
     call: IncomingCall,
     app_state: Weak<AppState>,