Fix clippy::for_kv_map lint violations (#36493)

Release Notes:

- N/A

crates/channel/src/channel_buffer.rs

@@ -135,7 +135,7 @@ impl ChannelBuffer {
             }
         }
 
-        for (_, old_collaborator) in &self.collaborators {
+        for old_collaborator in self.collaborators.values() {
             if !new_collaborators.contains_key(&old_collaborator.peer_id) {
                 self.buffer.update(cx, |buffer, cx| {
                     buffer.remove_peer(old_collaborator.replica_id, cx)

crates/channel/src/channel_store.rs

@@ -1073,7 +1073,7 @@ impl ChannelStore {
 
                 if let Some(this) = this.upgrade() {
                     this.update(cx, |this, cx| {
-                        for (_, buffer) in &this.opened_buffers {
+                        for buffer in this.opened_buffers.values() {
                             if let OpenEntityHandle::Open(buffer) = &buffer
                                 && let Some(buffer) = buffer.upgrade()
                             {