Don't allow dropping files on remote projects (#11218)

Release Notes:

- Fixed a panic when a remote participant dropped a local file on your
project

crates/project/src/project.rs

@@ -8525,11 +8525,13 @@ impl Project {
                     OpenBuffer::Weak(_) => {}
                 },
                 hash_map::Entry::Vacant(e) => {
-                    assert!(
-                        is_remote,
-                        "received buffer update from {:?}",
-                        envelope.original_sender_id
-                    );
+                    if !is_remote {
+                        debug_panic!(
+                            "received buffer update from {:?}",
+                            envelope.original_sender_id
+                        );
+                        return Err(anyhow!("received buffer update for non-remote project"));
+                    }
                     e.insert(OpenBuffer::Operations(ops));
                 }
             }