chore: Prepare for Rust edition bump to 2024 (without autofix) (#27791)

Successor to #27779 - in this PR I've applied changes manually, without
futzing with if let lifetimes at all.

Release Notes:

- N/A

crates/copilot/src/copilot.rs

@@ -348,7 +348,10 @@ impl Copilot {
         this
     }
 
-    fn shutdown_language_server(&mut self, _cx: &mut Context<Self>) -> impl Future<Output = ()> {
+    fn shutdown_language_server(
+        &mut self,
+        _cx: &mut Context<Self>,
+    ) -> impl Future<Output = ()> + use<> {
         let shutdown = match mem::replace(&mut self.server, CopilotServer::Disabled) {
             CopilotServer::Running(server) => Some(Box::pin(async move { server.lsp.shutdown() })),
             _ => None,