fix(flexes): reset flexes when collapsing axis

Co-authored-by: Mikayla Maki <mikayla@zed.dev>

crates/workspace/src/pane_group.rs

@@ -398,7 +398,9 @@ impl PaneAxis {
             }
 
             if self.members.len() == 1 {
-                Ok(self.members.pop())
+                let result = self.members.pop();
+                *self.flexes.borrow_mut() = vec![1.; self.members.len()];
+                Ok(result)
             } else {
                 Ok(None)
             }